Working at their respective constant rates, machine A makes 100 copies in 10 minutes and machine B makes 150 copies in 15 minutes. If these machines work simultaneously at their respective rates for 30 minutes, what is the total number of copies that they will produce?  Options.
A) 250	B) 600	C) 675	D) 700	E) 750

Rationale: "machine a can produce 100 * 30 / 10 = 300 copies and , machine b can produce 150 * 30 / 15 = 300 copies total producing 600 copies . b is the answer"
Answer: B