Question 852794
Let me use a different variable.
w for width
y for length


y=w+12 for length
and still w for width


Area for the base:  {{{(w-2*4)((w+12)-2*4)=(w-8)(w+4)}}}
Volume for the box:  {{{highlight(4(w-8)(w+4)=112)}}}
NOW it is setup.  Solve for w.