Question

What is the value of the x variable in the solution to the following system of equations?
7x - 2y = 21
4x + y = 57

21

-21

9

-9

Answer 1

7x - 2y = 21
4x + y = 57

Multiply everything in the bottom equation by 2 and you get:

7x - 2y = 21
8x + 2y = 114

Then add both equations together and you get:

15x = 135

Then divide both sides by 15 and you get x = 9

Answer 2

7x - 2y = 21---------- A

4x + y = 57 ---------- B
--------------------------------
A + 2*B
--------------------------------


7x - 2y = 21
+
8x + 2y = 114
-------------
15x =135
x = 9 --------------- put this value in eq B

4*9 + y = 57
y = 57-36
y=21