System of equation by using substitution
3=y+3x
-x+3y=29

x=-2

y=9

Step-by-step explanation:

3=y+3x A

-x+3y=29 B

step 1. rearrange equation A, so you have the "y" variable on one side

3=y+3x

-3x     -3x

3-3x=y

y=3-3x C

step 2. Substitute equation C into equation B in place of "y"

-x+3(3-3x)=29 ---foil

-x+9-9x=29 -- collect like terms

-10x+9=29

       -9     -9

   -10x=20

      ÷-10     ÷-10

         x=-2

Step 3. Substitute x=-2 into equation C to find y

y=3-3(-2)

y=3+6

y=9

Check you answer by subsituting x=-2 and y=9 back into equation A and B