How do you solve x -7y=16 and -3x+6x= -3 using substitution?

1 Answer
May 30, 2017

The final answer is x=-1 and y=-17/7

Explanation:

To use substitution, we must isolate x on one of the sides in one of the equations. The first equation looks simple enough to manipulate and isolate x.

We can add 7y to both sides of the first equation to get:

x = 7y + 16

Now, we can turn towards the second equation. We can first simplify the left side by adding the x's ( -3x and 6x) to make the second equation:

3x = -3

Although we could just solve for x here, we should use substitution. We can know replace x with the equal value 7y + 16 (from the first equation) to make the second equation:

3(7y + 16) = -3

Now we can solve the second equation from there by distributing, subtracting, and dividing:

21y + 48 = -3
21y = -51
y = -51/21 = -17/7

To solve for x, we can substitute our value for y into the first equation (x = 7y + 16) to get:

x = 7(-17/7) + 16
x = -17 + 16
x = -1.

Therefore, our final solution is x=-1 and y = -17/7