One cylinder has a volume that is 8 cm³ less than 7/8 of the volume of a second cylinder. if the first cylinder’s volume is 216 cm², what is the correct equation and value of x, the volume of the second cylinder

Let's say the cylinders are 
A = first cylinder
B = second cylinder

B has some volume, the volume is  "x"
what's 7/8 of "x"?  well (7/8)x
what's 8 less than that?  well (7/8)x - 8

A has a volume of 216
we also know that, A's volume is (7/8)x - 8

thus