Question 926122
Try to draw a picture.


L for length, w for width.
L=w+15.
Height will be same as the edge of one of the removed squares, 5 inches.


Base of the box will be {{{(L-2*5)(w-2*5)}}}
{{{(w+15-2*5)(w-2*5)}}}
{{{(w+5)(w-10)}}}


The expression for the volume is {{{5(w+5)(w-10)}}}.
This is the given volume value;
{{{highlight(5(w+5)(w-10)=1250)}}}.
Solve that for w.