Cian is buying movie tickets for a group. He wants to have at least 30 tickets and spend no more than $400. Adult tickets cost $12.50 and child tickets cost $7.50. Which system of inequalities can be used to find the number of each type of ticket Cian could buy?

A. x + y ≥ 30
7.5x + 12.5y ≤ 400

B. x + y ≤ 30
7.5x + 12.5y ≥ 400

C. x + y ≥ 30
7.5x + 12.5y ≥ 400

D. x + y ≤ 30
7.5x + 12.5y ≤ 400​