Question
-x - y = 0
6x - 5y = 66
Step one, name the two equations
-x -y = 0 .................................................1
6x - 5y = 66 ..............................................2
Step 2, choose one of the equation, make one of the variable subject of formula and substitute in the second equation.
-x - y = 0
y = -x
Subtitute y in equation 2
6x - 5(-x) = 66
6x + 5x = 66
11x = 66
divide through by 11
x = 66/11
x = 6
since y = -x
y = -6