Robert has 45 dollars. He buys 6 tshirts and has 7 dollars left over. How much did each tshirt cost?

Let x be the price of one t-shirt. Set up an equation:
6 times the number of t-shirts plus 7 dollars left over get him to a total of 45
6x = 45 - 7
6x = 38

Divide each side by 6
x = 6.33