To find the cost of the fence, apply the formula $\displaystyle \small P=2(width)+2(length)$ in order to first find the length of the perimeter of the fence.

Then multiply the perimeter by $\displaystyle \small \$12.50$.

Thus, the solution is:

$\displaystyle \small P=2(15)+2(8)$
$\displaystyle \small P=30+16$
$\displaystyle \small P=46$

$\displaystyle \small 46\times12.5=575$ 

To solve this problem apply the formulas: $\displaystyle \small Area=width\times length$ & $\displaystyle \small Perimeter=2(w)+2(l)$

Thus, the solution is:

$\displaystyle \small A=14\times4=56$
$\displaystyle \small P=2(14)+2(4)=28+8=36$

The legs of a right triangle are its base and height, so use the area formula for a triangle with these dimension. Setting $\displaystyle b=16,h=90$:

$\displaystyle A = \frac{1}{2} bh = \frac{1}{2} \cdot 16 \cdot 90= 720$

Use the area formula for a triangle, setting $\displaystyle b=18,h=14$:

$\displaystyle A = \frac{1}{2} bh = \frac{1}{2} \cdot 18 \cdot14 = 126$

The two legs of a right triangle can serve as its base and its height. The area of the triangle is half the product of the two:

$\displaystyle \frac{1}{2} \cdot 7 \cdot 24 = 84$

That is, the area is 84 square inches.

The two legs of a right triangle can serve as its base and its height. The area of the triangle is half the product of the two:

$\displaystyle \frac{1}{2} \cdot 50 \cdot 120 = 3,000$

That is, the area is 3,000 square millimeters.

The area of a triangle is one half the product of its base and its height - in the above diagram, that means

$\displaystyle A = \frac{1}{2}xy$.

Substitute $\displaystyle A = 450, x = 20$, and solve for $\displaystyle y$ :

$\displaystyle \frac{1}{2} \cdot 20 \cdot y = 450$

$\displaystyle 10 \cdot y = 450$

$\displaystyle 10 \cdot y \div 10 = 450 \div 10$

$\displaystyle y = 45 \textrm{ cm}$

To find the area of a triangle, multiply the base of the triangle by the height and then divide by two.

$\displaystyle 10*12=120$ 

$\displaystyle 120/2=60$

The area of the entire square is the square of the length of a side, or

$\displaystyle 80 \times 80 = 6,400$.

The area of the white right triangle is half the product of its legs, or

$\displaystyle \frac{1}{2} \times 30 \times 60 = 900$.

Therefore, the area of that triangle is 

$\displaystyle \frac{900 }{6,400} \times 100 = 14 \frac{1}{16} \%$

of that of the entire square.

The area of a triangle is half the product of its base and its height, so Mr. Jones's parcel originally had area 

$\displaystyle \frac{1}{2} \times 140 \times 160 = 11,200$ square meters.

The portion he sold his brother, represented by the red right triangle, has area

$\displaystyle \frac{1}{2} \times 56 \times 128 = 3,584$ square meters.

Therefore, the area of the parcel Mr. Jones retained is 

$\displaystyle 11,200 -3,584= 7,616$ square meters.