Given that the dimensions are: , , and  and that the volume of a rectangular prism can be given by the equation:

, where  is length,  is width, and  is height, the volume can be simply solved for by substituting in the values.

This final value can be approximated to .

The volume of a rectangular prism is found using the following formula:

If we substitute our known values, then we can solve for the missing side.

Divide both sides of the equation by 12.

We now know that the missing length equals 7 centimeters.

This means that the box can have sides with the following dimensions: 3cm by 4cm; 7cm by 3cm; or 7cm by 4cm. The greatest area of one side belongs to the one that is 7cm by 4cm. 

The volume of the rectangle 

so we plug in our values and obtain

.

A regular tetrahedron has 4 triangular faces. The area of one of these faces is given by:

Because the surface area is the area of all 4 faces combined, in order to find the area for one of the faces only, we must divide the surface area by 4. We know that the surface area is , therefore:

Since we now have the area of one face, and we know the height of one face is , we can now plug these values into the original formula:

Therefore, the length of the base of one face is .

The only given information is the surface area of the regular tetrahedron.

This is a quick problem that can be easily solved for by using the formula for the surface area of a tetrahedron:

If we substitute in the given infomation, we are left with the edge being the only unknown. 

The problem provides the information for the slant height and the area of one of the equilateral triangle faces. 

The slant height merely refers to the height of this equilateral triangle. 

Therefore, if we're given the area of a triangle and it's height, we should be able to solve for it's base. The base in this case will equate to the measurement of the edge. It's helpful to remember that in this case, because all faces are equilateral triangles, the measure of one length will equate to the length of all other edges.

We can use the equation that will allow us to solve for the area of a triangle:

where  is base length and  is height.

Substituting in the information that's been provided, we get:

This becomes a quick problem by just utilizing the formula for the volume of a tetrahedron. 

Upon substituting the value for the volume into the formula, we are left with , which represents the edge length. 

The problem states that the volume is:

The point of the problem is to solve for the length of the edge. Becasuse there are no numbers, the final answer will be an expression. 

In order to solve for it, we will have to rearrange the formula for volume in terms of . 

The diagonal of a shape is simply the length from a vertex to the center of the face or vertex opposite to it. With a regular tetrahedron, we have a face opposite to the vertex, and this basically amounts to calculating the height of our shape.

We know that the height of a tetrahedron is  where s is the side length, so we can put  into this formula:

which gives us the correct answer.

Write the formula for finding the surface area of a tetrahedron.

Substitute the edge and solve.