While both types of interest will grow your money over time, there is a big difference between the two. Specifically, simple interest is only paid on principal, while compound interest is paid on the principal plus all of the interest that has previously been earned.
18.84 because the formula to find the volume of a cone is pie*r^2*h/3 and your radius is 3 and the height is 2, so if you plug those in the equation and calculate it this should be your answer