It takes 40 identical printing presses 12 hours to print 500,000 papers. How many hours would it take 30 of these printing presses to print 500,000 papers? Choose the correct choice from the following answers:  A) 14  B) 15  C) 16  D) 18  E) 20

Rationale: "40 printing presses can do 1 / 12 of the job each hour . 30 printing presses can do 3 / 4 * 1 / 12 = 1 / 16 of the job each hour . the answer is c ."
Answer: C