How do I solve this using substitution

Question

What is the x-coordinate of the solution for the system of equations?

y−x=9

10+2x=−2y

 

I  turned y-x=9 into y=x+9 and plugged it into 10+ 2x=-2y to get 10 + 2x= -2 (x+9). Im not sure what to do after this.

Answer 1

10 + 2x= -2 (x+9)      where you stopped correctly

10 + 2x = -2x - 18      distribute

10 + 4x = - 18            add 2x to both sides

4x = -28                     subtract 10 from both sides

 

You get to do the last step.