Solve for x: 21 + 7(3x-3) = 9(3x+3) - 15

We'll move all terms of the given equality to one side,
changing their signs.

21 + 7(3x-3) - 9(3x+3) + 15=
0

Now, we'll remove the
brackets:

21 + 21x - 21 - 27x - 27 + 15 =
0

We'll combine and eliminate like
terms:

-6x - 12 = 0

We'll
subtract 12 both sides:

-6x =
12

We'll divide by -6 both
sides:

x
=-12/6

x =
-2

Another way to solve the proble would be
to factorize by 21, the left side:

21(1+x-1) =
3(9x+9-5)

We'll divide by 3 both
sides:

7x = 9x + 4

We'll
subtract 9x both sides:

-2x =
4

We'll divide by
-2:

x =
-2