Working at their respective constant rates, machine A makes 100 copies in 15 minutes and machine B makes 150 copies in 10 minutes. If these machines work simultaneously at their respective rates for 30 minutes, what is the total number of copies that they will produce?
Choose the correct choice from the following answers
A) 250 B) 425 C) 650 D) 700 E) 750

Rationale: "machine a can produce 100 * 30 / 15 = 200 copies and , machine b can produce 150 * 30 / 10 = 450 copies total producing 650 copies . c is the answer"
Answer: C