Solve using substitution.
10x − 10y = 20
–5x + y = 18
From the second equation, solve for y:
y = 5x + 18
Now substitute this into the first equation:
10x - 10(5x + 18) = 20
10x - 50x - 180 = 20
-40x - 180 = 20
-40x = 200
x = -5
Now substitute x back into the equation to solve for y:
-5(-5) + y = 18
25 + y = 18
y = -7
Therefore, the solution is x = -5 and y = -7.