Linear equations-transposition of formulae why does this turn into this

Is δ pmr similar to δ smn ? if so, which postulate or theorem proves these two triangles are similar?

Ahome improvement store rents it’s delivery truck for $19 for the first 75 minutes and $4.75 for each additional 1/4 hour. if a customer rented the truck at 11: 10 am and returned the truck at 1: 40 pm the same day, what would his rental cost be?

Atriangular field has sides of lengths 21, 39, and 41 yd. find the largest angle. (round your answer to the nearest degree.)