Let x represent the cost of a slice of pizza and let y represent the cost of a hamburger. 7 hamburgers and 3 slices of pizza cost $19, i.e. the $20 you paid minus the $1 change. 8 hamburgers and 2 slices of pizza cost $19.50. So:
3x+7y=19 and 2x+8y=19.5
Solve the system for the values of and . Multiply by 3 and multiply by 5, then add the two products. Subtract the sum from $20 for your answer.
