Explanation:
2 equations with 2 variables can be solved in 2 relatively different ways :
1. by elimination (we multiply if needed the equations by certain factors, so that when adding both equations one variable is eliminated).
2. by substitution : we use one equation to express one variable by the other, which we then used in the second equation.
in both cases we then solve for the one remaining variable. and then we use one of the other equations to solve for the second variable.
since the equations are so similar already, we use the first approach. we don't need to multiply anything by a factor, the terms in x are the same with different signs, so we just add both equations :
-x + 6y = 9
+ x + 6y = -3
-------------------
0 12y = 6
y = 6/12 = 1/2 = 0.5
x + 6×1/2 = -3
x + 3 = -3
x = -6
FYI - how would substitution work ?
e.g.
x + 6y = -3
x = -3 - 6y
that we use now in the other equation
-(-3 - 6y) + 6y = 9
3 + 6y + 6y = 9
3 + 12y = 9
12y = 6
y = 6/12 = 1/2 = 0.5
and then
-x + 6×1/2 = 9
-x + 3 = 9
-x = 6
x = -6