First, let's assign variables to the names of the individuals to represent their age in 2013. 

In 2013, Molly was three times older than Steve; therefore, we can write the following expression:

We are also told that in 2016, Molly will be two times older than Steve; thus, we can write another expression: 

.

We can then substitute  in for  in the second equation to arrive at the following:

Using the given information we can generate the following two proportions:

 and

Next, cross-multiply each proportion to come up with the following two equations: 

 and  

Each equation shares a term with the  variable. We need to make this variable equal in both equations to continue. Multiply the first equation by a factor of 3 and the second by a factor of 2, so that the  terms are equivalent. Let's start with the first equation.

Now, we will perform a similar operation on the second equation.

Now, we can set these equations equal to one another.

Drop the equivalent  terms.

 The proportion then becomes the following: 

 or 

Assign a variable to science books since everything in the question can be written in terms of science books.

Write an expression for the phrase "twice as many comic books as science books."

To create an equation for the cost of the books, we can write the following:

Substitute in the known values and variables.

Jeff purchased 2 science books and 4 comic books.

In general for work problems:  W₁ + W₂ = 1 where Work = Rate x Time

Note, 1 represents the completed job assignment.

For example, W₁ is the rate that the first person would finish the job multiplied by the time it would take two or more people to finish the job completely.

1/3x + 1/2x = 1 where x is the time it would take for both people to complete the job.

Find a common denominator to add the fractions, then solve for x.

x = 1.2 days for one house, but the questions asks about two houses, so the correct answer is 2.4 days.

Property area = 10,000 ft x 40,000 ft = 400,000,000 ft²

Acreage = 400,000,000 ft² / 43,560 ft² per acre = 9,183 acres

Taxes = $3.50 per acre x 9,183 acres = $32,140

Remember that distance = rate x time

For the first route, we can set up an equation where the total distance (36 + 44) equals the rate (65 mph) multiplied by the time:

36 +44 = 65t

80 = 65t

t = 80/65 = 1.23 hrs = 1 hr, 14 min

To find the time taken for the second route, we first figure out the distance traveled by using the Pythagorean Theorem.

We know that the "legs" of the right triangle are 44 and 36, where the hypotenuse is the straightline distance (northwest), directly to the destination:

a²+b²=c²                                                                                                       

44²+36²=c²                                                                              

3232=c²                                                                                     

c=56.85

56.85=40t

56.85/40=t

t=1.42 hrs=1 hr, 25 min                                                         

1 hr. 25 min. – 1 hr. 14 min. = 11 min.

To calculate miles per gallon of gas, we take the 478 miles the motorcycle travels and divide it by the amount of gallons in a full tank of gas, 12 gallons.  478/12 = 39.83, or 39.8 when rounded to the tenths place

For the price, we take the 12 gallons and multiply it by the amount that one gallon costs, $4.25.  (12)(4.25) = 51

First we determine how many gallons it will take to travel 3,149 miles with this particular car: 3,149/31=101.58 gallons. The cost of gas per gallon= $3.69, therefore 101.58x$3.69= $374.83.

We divide 1,457 miles by 47 miles per gallon to find that 31 gallons of gas are needed for the road trip.

We then multiply the gallons of gas by the cost per gallon to find: 

31 x 4.13 = 128.03

First, we need to convert the 1 hour into minutes in order to keep consistent with units -- so, the car averages 32 miles per 60 minutes.  Then, a ratio can be set up to solve this: 32 mi / 60 min = x mi / 20 min. Cross multiplying and dividing, we get x = 10.667 miles.  Rounding to the nearest tenth, this becomes 10.7 miles.