### Home > GC > Chapter 6 > Lesson 6.1.2 > Problem 6-17

6-17.

Set up equations that represent the information you are given.

What is the sum of the angles within a triangle?

How can you use this to find ∠*B*?

One you know m∠*B*, solve for angles *A* and *C*.

m∠*A* = 3m∠*B* + 5°

m∠*C* = m∠*B* − 20°

m∠*A* + m∠*B* + m∠*C* = 180°

Substitute.

(3m∠*B* + 5°) + m∠*B* + (m∠*B* − 20°) = 180°

Solve for *B*.