precalc question

Question

Jane can sand and refinish the hardwood floor in a certain room in 25 hours. Together with her co-worker, Alex, they can sand and refinish this room's floor in 24 hours. How many hours would it take Alex working by himself to sand and refinish this floor?

Round your answer to 2 places after the decimal point (if necessary) and do NOT type any units (such as "hours") in the answer box.

Time for Alex to sand and refinish this floor: 

Answer 1

1/25 + 1/x = 1/24; x = 25·24/(25 - 24) = 600 hours