y-2x=3 and -x=y-9 use the substitution method to solve the system on equations.

using y - 2x = 3 

We get that y = 2x + 3

Substitute that into the second equation 

-x = (2x+3) - 9 

-x = 2x - 6 

6 = 3x 

x = 2 

and 

y = 7