Christopher swam laps everyday in the town swimming pool. he swam 45 minutes each day, five days each week, for twelve weeks. in that time, he swam 1800 laps. what was his average rate in laps per hour

This is simple conversion.
Start from getting the numbers of hours.
12 weeks × 5 days × 45 minutes will get the number of minutes spent total (2700mins). Divide this by 60 min to get the number of hours spent total - 45 Hours.

to get the rate - r=laps/time
1800laps/45 hours
rate = 40laps/hour