Answer: $7
Step-by-step explanation:
Let x = Cost of each T-shirt.
As per given,
Total charge =( Number of t shirts x Cost per t shirt )+ set up fee
For 21 T-shirts , total charge would be : 21x+40
According to the question
⇒21x+40=187
⇒21x = 187-40
⇒21x = 147
⇒x= 7
Hence, each T-shirt costs $7 .