To solve for y in the equation 2x - y = 8, we need to substitute the given value of x = -1 into the equation and solve for y.
Replacing x with -1 in the equation, we have:
2(-1) - y = 8
Simplifying:
-2 - y = 8
Now, let's isolate y by moving the constant term to the other side:
-y = 8 + 2
-y = 10
To solve for y, we can multiply both sides of the equation by -1, which will change the sign:
y = -10
Therefore, when x = -1, y = -10.