check the picture below.
[tex]\bf (y+16)^2=(y-56)^2+y^2
\\\\\\
\underline{y^2}+32y+16^2=y^2-112y+56^2+\underline{y^2}
\\\\\\
32y+256=y^2-112y+3136\implies 0=y^2-144y+2880
\\\\\\
0=(y-24)(y-120)\implies y=
\begin{cases}
\boxed{120}\\
24
\end{cases}[/tex]
it cannot be 24, because then the ground base area will be 24 - 56, which is a negative amount and unfeasible for the phenomena.
