Hello! First off, we can find the unit rate on what it would cost per pizza. Divide the total amount by the number of pizzas. 10.50/3 is 3.5. It costs $3.50 per medium pizza. Now, we can multiply that amount by 10 to get the amount for 10 pizzas. 3.5 * 10 is 35. There. It costs $35 to buy 10 medium pizzas.