Solve any algebraic expression by getting the x on one side (usually the left-hand side) and everything else and the opposite side (usually the right-hand side).
We do this by using the inverse operation of what is being done to the variable. If something is adding to the variable, say like an expression like x + 10, then we use subtraction to get rid of the addition and vice versa.
Similar to multiplication, we use division to cancel out the multiplication and vice versa.
If there are any like terms, we combine them. I will assume that you know how to combine like terms, but in short, to combine like terms, add the coefficients together and use the common variables and power. If there is no coefficient, then a 1 is implied. Similarly, if no explicit power is shown, then a 1 is implied.
-6x - 2x = 40
-8x = 40
-6x and -2x are like terms because they have the same variable and are to the same power.
-6x + (-2)x
(-6 - 2)x
-8x
Now we have the expression -8x = 40. Now we can use division to get rid of the -8 juxtaposed to the variable x.
-8x = 40
-8x / 8 = 40 / -8
x = -5