He swam 1,800 laps total, in 12 weeks.
Each week, he swam 1800/12 = 150 laps, in 5 days.
Each day, he swam 150/5 = 30 laps, in 45 minutes.
His average time was (30 laps) / (45 minutes)
= (30/45) (lap/minute)
= 2/3 lap/minute .
At that rate, in one hour, he would swim
(2/3 lap/minute) x (60 minute/hour)
= (2/3 x 60) (lap/hour) = 40 laps/hour .
Let's check that:
(40 lap/hour) x (0.75 hour/day) x (5 day/week) x (12 weeks)
= (45 x 0.75 x 5 x 12) x (laps) = 1,800 laps yay !