What is the sum of angle measures in a 42-gon

Suppose that an airline uses a seat width of 16.516.5 in. assume men have hip breadths that are normally distributed with a mean of 14.414.4 in. and a standard deviation of 0.90.9 in. complete parts (a) through (c) below. (a) find the probability that if an individual man is randomly selected, his hip breadth will be greater than 16.516.5 in. the probability is nothing. (round to four decimal places as needed.)

Given: m∠ adb = m∠cdb ad ≅ dc prove: m∠ bac = m∠bca lol

Having a hard time understanding this question (see attachment).