Question

Which system of equations would be best solved using Substitution?

1.
2x = 10
y= -3

2.
-2x + 5y = -1
2x +5y = 11

3.
y = 2/3x + 5
2x - 6y= -42

4.
3x + 7y = 21
-4x - 3y = -9

Answer 1

3.

Reason: y is already isolated (y = (2/3)x + 5), so substitute that expression into the second equation:
2x − 6( (2/3)x + 5 ) = −42
2x − 4x − 30 = −42
−2x = −12 → x = 6
Then y = (2/3)(6) + 5 = 4 + 5 = 9.