Just steps on how to solve part B thanks

The tile along the edge of a triangular community pool needs to be replaced? ?

Given: m zade = 60° and m2cdf = (3x + 15) prove: x = 15

David and alton are training for a race. they spend 35 minutes stretching and then go on a 5 mile practice run. david runs at a pace of 7 min/mile. alton runs at a pace of 8 min/mile. write an equation for each runner that shows the total length of their workout. then solve each equation showing your work