I did this a little differently.
It takes 480 mins to fill 3/5 of the pool.
We're trying to find out how long it'll take for the remaining 2/5.
I solved how many minutes it'll take to fill the pool to 1/5 capacity and multiplied it by 2.
480 / 3 = 160 mins (1/5 full)
160 * 2 = 320 mins (2/5 full)
320 mins = 5 hours 20 mins
It takes 480 mins to fill 3/5 of the pool.
We're trying to find out how long it'll take for the remaining 2/5.
I solved how many minutes it'll take to fill the pool to 1/5 capacity and multiplied it by 2.
480 / 3 = 160 mins (1/5 full)
160 * 2 = 320 mins (2/5 full)
320 mins = 5 hours 20 mins