Substitution using inequalities

How to solve with substitution

y=2x+4

3x+y=9

3x+(2x+4)=9

3x+(2x+4)=9

5x+4=95x+4=9

5x=55x=5

x=1

Miconceptions

Re-arranging the equation and then substituting it back into itself. This will make everything cancel out.

Incorrect: 2x + 3y = 4 rearranging x−5y=6→ x−5y=6 x = 5y + 6 Puttingitbackintoitself... 5y+6−5y=6 6=6 0=0

How to solve

just replace the x or y in one equation with what x or y equals in the other
Substitution method