Pipes A and B working together can fill a tank in 4 hours. If they operate individually, pipe B takes 6 hours longer than pipe A to fill the tank. How long does pipe A require to fill the tank alone?

Explanation

Assume pipe A fills the tank in x hours. Then pipe B fills it in (x + 6) hours. Their combined rate is 1/4 tank per hour, so: 1/x + 1/(x + 6) = 1/4. Solving this equation gives x = 6 hours, meaning pipe A alone takes 6 hours to fill the tank.