Add mn to each side:

ax - mn + mn = mn + bx + mn

Cancel the mn terms on the left side and we get:

ax = bx + 2mn

Subtract bx from each side:

ax - bx = bx - bx + 2mn

Cancel the bx terms on the right side:

ax - bx = 2mn

Factor out x on the left side:

x (a - b) = 2mn

Divide each side of the equation by (a - b):

x (a - b)/(a - b) = 2mn/(a - b)

Cancel the (a - b) on the left side and we get:

x =

**2mn/(a - b)**