Answer:
3.50
Step-by-step explanation:
6(2) = 12
6(2.50) = 15
6(3) = 18
6(3.50) = 21
If he paid $21 for 6 t-shirts and each t-shirt was the same price...then the cost of 1t-shirt was $3.50. If you want to double-check this, divide $21.00 by $3.50 and you should get 6 as the answer!
