b - 9 + 6b = 30
You need to add all the b's up on the left side of the equation first. So it rewrites like this:
7b - 9 = 30
next you add 9 to each side to get 7b alone on the left side.
7b = 39
now divide both sides by 7 so that b is all by itself.
b = 5 4/7 or 5.57
