You need to isolate the B variable, so here are the steps:
25 + 3b - 11 = 75 --> subtract 25 from both sides 3b - 11 = 50 --> add 11 to both sides 3b = 61 --> divide both sides by 3 to get b by itself b = 20.33 (decimal form) or b = 20 1/3 (fraction form)
