<span>B) 84 + z = 180, since 42*2=84, 180-84=96, z=96</span>
Take the as together and take the bs together.
5a + 3b - 6a - b.
5a - 6a + 3b - b. Then simplify.
-a + 2b.
That's it.
Divide both sides by -3, and replace
with
. Then

Factorize the quadratic in
to get

which in turn means

But
for all real
, so we can ignore the first solution. This leaves us with

If we allow for any complex solution, then we can continue with the solution we ignored:
