Since the formula for the base of the cylinder is

, multiplying that by 10 we get

. Hope this helps!
For #16, it can be assume that the two angles are linear, so set them both equal to 90 (9x+x-10=90) and solve for x. Once you have x, plug it into the equations to find the measure of both angles. If both your final answers are added, they should equal 180. If not, go back and try to find where you messed up.
B= the square root of 65
Formula: a^2= c*2-b^2
a^2= 81-16= 65
Once you find the square root of 65, thats your answer, but here they want you to keep it as 65.
Hope this helps!
(-x^2+4)
x^2y^3-2y^3-2x^2+4=x^2-2x^2+4=
(-x^2+4)