Jika 5x +2y= -3 dan 7x + 8y = -1 berapakah nilai dari 4x + 2y?

5x + 2y = -3
7x + 8y = -1

35x + 14y = -21
35x + 40y = -5
--------------------   -

-26 y = -16
y = 8/13

5x + 2y = -3
5x + 2 (8/13) = -3
5x + 16/13 = -3
5x = -39/13 - 16/13
5x =  -55/13
x   = -55/13 × 1/5
x   = -11/13

4x + 2y
4 × -11/13 + 2 × 8/13
-44/13 + 16/13
- 28/13