Multiply the amount of shoes being bought (7) by the price of one pair of shoes (15):
7(15) = $105 with NO discount
If you have 10% off that means that you will be paying 90%. Multiply 90% or 0.9 by the cost of the seven shoes:
0.9(105) = 94.50
You will pay $94.50 for the seven pairs of shoes.