Solve each system by substitution. See Example 1.
7. 4x + 3y = -13
-x + y = 5
8. 3x + 4y = 4
x - y = 13
9. x - 5y = 8
x = 6y
10. 6x - y = 5
y = 11x
11. 8x - 10y = -22
3x + y = 6
12. 4x - 5y = -11
2x + y = 5
13. 7x - y = -10
3y - x = 10
14. 4x + 5y = 7
9y = 31 + 2x
15. -2x = 6y + 18
-29 = 5y - 3x
16. 3x - 7y = 15
3x + 7y = 15
17. 3y = 5x + 6
x + y = 2
18. 4y = 2x - 4
x - y = 4
Solve each system by elimination. In systems with fractions, first clear denominators. See Example 2.
19. 3x - y = -4
x + 3y = 12
20. 4x + y = -23
x - 2y = -17
21. 2x - 3y = -7
5x + 4y = 17
22. 4x + 3y = -1
2x + 5y = 3
23. 5x + 7y = 6
10x - 3y = 46
24. 12x - 5y = 9
3x - 8y = -18