Question:
Evaluate each expression:
1. 9x + 8y, when x = 4 and y = 5
2. 2x + 8x, when x = 3
3. 4y + 7y, y = 5
4. 10x + 18y, when x = 4 and y = 5
5. x + 8y, when x = 2 and y = 1/4
6. 9x + 8y, when x = 1/3 and y = 1/4
7. 3x + 7y, when x = 8 and y = 4
8. 12x + 16y, when x = 1/4 and y = 5