Answer :
[140=15x-520
+520 +520
____________
660=15x
660/15=15x/15
x=44
44 t shirts does the t shirt shack need to sell to make a profit of $140
+520 +520
____________
660=15x
660/15=15x/15
x=44
44 t shirts does the t shirt shack need to sell to make a profit of $140