Question 1003693
Call the costs of the shirts x and y.<P>
x + y = 57 and x = y+18<P>
Substitute the second equation into the first for x.<P>
y + 18 + y = 52<P>
2y = 34<P>
y = 17<P>
x = y + 18 = 17 + 18 = 35.  The more expensive shirt was $35.