at a ballpark, the price of popcorn includes sales tax. the cost of 3 large popcorns and 7 medium popcorns is $65.45. the cost of 5 large popcorns and 3 medium popcorns is $59.25. if I is the cost of a large popcorn and m is the cost of a medium popcorn, write a system of equations that models this situation