How can we solve ax + z = aw - y for a

        ax + z = aw - y
ax - aw + z = -y                        Subtract aw from both sides.
      ax - aw = -y - z                   Subtract z from both sides.
      a(x - w) = -y - z                   Factor ax - aw.
                a = (-z - y)/(x - w)      Divide x - w froem both sides.
                a = (-1(y + z))/(x - w)  Change the solution.
                a = -(y + z)/(x - w)