[ton of points] [3 questions - easy money : )] basic geometry questions! will mark brainleist!

The correct answers are:

1/6πd³;
3; and 
9 cm.

Explanation:

For the first question:

The formula for the volume of a sphere is:



We have the diameter, not the radius.  The diameter is twice as much as the radius; this means to find the radius using the diameter, we divide by 2.  This gives us:



When we raise a fraction to a power, we raise both the numerator and the denominator to that power.  This gives us:



We start multiplying this:


For the second question:

The planes of symmetry are the planes through which we can fold the figure in half.  These are in the middle horizontally through the figure; in the middle vertically (through the width) through the figure; and in the middle vertically (through the length) through the figure.  This makes 3.

For the third question:

The formula for the volume of a triangular prism is:

,

where b is the base of the triangular base of the pyramid, h is the height of the triangular base of the pyramid, and H is the height of the pyramid.

We know the volume is 90; the base of the triangle is 12 and the height is 5:



We divide both sides by 10:

90/10 = 10H/10
9 = H