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
[tex]\bf \textit{A's volume}=
\begin{cases}
216\\
\frac{7}{8}x-8
\end{cases}\implies 216=\cfrac{7}{8}x-8\impliedby
\begin{array}{llll}
multiplying\\
by\ 8
\end{array}
\\\\\\
1728=7x-64\implies 1728+64=7x\implies \cfrac{1792}{7}=x\implies 256=x[/tex]