First, subtract color(red)(z) and color(blue)(aw) from each side of the equation to isolate the a terms while keeping the equation balanced:
ax - color(blue)(aw) + z - color(red)(z) = aw - color(blue)(aw) - y - color(red)(z)
ax - aw + 0 = 0 - y - z
ax - aw = -y - z
Next, factor an a from each term on the left side of the equation:
a(x - w) = -y - z
Now, divide each side of the equation by color(red)(x - w) to solve for a while keeping the equation balanced:
(a(x - w))/color(red)(x - w) = (-y - z)/color(red)(x - w)
(acolor(red)(cancel(color(black)((x - w)))))/cancel(color(red)(x - w)) = (-y - z)/(x - w)
a = (-y - z)/(x - w)
We can then multiply the right side of the equation by a form of 1 to rewrite the expression as:
a = (-1)/-1 xx (-y - z)/(x - w)
a = (-1(-y - z))/(-1(x - w))
a = (y + z)/(-x + w)
a = (y + z)/(w - x)