1. substitution x+y=8, x−y=−4
2. substitution 3x−4y=−30, 3x+2y=6
3. substitution −4x+9y=9, x−3y=−6
4. substitution 12x+13y=9, 15x−23y=6
5. substitution −2a+3b=14, a−4b=3
6. substitution 3x−7y=27, −5x+4y=−45
7. substitution 3x−4y=100, x3 +4y3 =100
8. substitution y=3x−4, y=32 x−2
9. substitution x2 −y2 =−1, x+4y=−12
10. substitution 12 x+17 y=4, 16 x−27 y=−1