if the t-shirts cost $8 to make, and the band sells them for 20$ they make a profit of $12 a shirt.
if after the concert, their profit is 304$ then I believe the way to solve it would be 304/12 which equals 25.3
However, they did not make a profit off of the 10 shirts that they gave away. 10*12 equals 120
304-120 equals 184
184/12 equals 15.
Your answer should be either 25 or 15