We are given this

write it as the difference of cubes

use the formula for the difference of cubes

Now use the formula for the difference of squares as 

1.) x=4
2.)? 20=32-50
3.)x= 16 divided by 4,3+1, etc.
Answer:
is the a. Perpendicular lines form 90° angles.
c = circumference
pi = 3.14
r = radius = 9 inches
d = diameter
c=pi*d
The radius is half of the diameter, d = 2r. Then d = 2*9=18.
plug into equation. c= pi*d = 3.14*18
round accordingly and you may want to include that the measurement you end up with is in inches.