Question

find the distance travelled in 1 h 40 min at a speed of 90 km/h

Answer 1

90 km/h is your constant.
1h 40m - 1h since we have 90 km/h.
2/3 of 90 is what we need to find for the 40 min, since 40m/60m = 2/3.
60 is 2/3 of 90.
90 + 60 = 150.
Your distance traveled is 150km.