instead of multiplying x+3 on both sides, I would instead subtract 2 on both sides. If you do this, it would be easier to write this equation in standard form and find the intervals.
Let n be the number. The difference of the number and six is n-6. Then three times the difference of the number and six is 3·(n-6). This number 3·(n-6) increased by four times the number n, then
