How to show your work to solve 3r^2-16r-7=5

OK so   3r^2-16r-7=5
Subtract five from both sides
3r^2-16r-7-5=0
Add like terms
3r^2-16r-12=0
Factorise it, this means putting it into brackets
(3r + 2)(r - 6)
Find out what multiplies to make negative twelve but adds to make negative sixteen
However none of the terms do this so we put negatives next to the "r"s
(-3r + 2)(-1r - 6)
The answer is r=6