In 5th grade terms

Divide the total time by 8. That's the time per trip.

is the answer 40

A bus route crosses the city 8 times in 12 hrs. On average, about how many minutes does it take the bus to cross the city?

12 hours/ 8 = 7200 minutes/8
Do the division.

No it is not 40. Let's see: 12 hrs times 60 minutes= 720 minutes. Divide 720 by 8 to get 90