Solve the following math problem step by step. The last line of your response should be of the form Answer: \boxed{$Answer} where $Answer is the answer to the problem.

<image>In the figure, $ m ∠1 = 3a + 40 $, $ m ∠2 = 2a + 25 $, and $ m ∠3 = 5b - 26 $. Find $b$.