You can put this solution on YOUR website! distance = 90 km
time = 45 minutes
speed = distance over time
= 90/45
= 2 km per minute
speed = 2 km per minute
it means it can travel 2 km in one minute
In an hour ( i.e 60 minutes ) it can travel = 2 km *60
= 120 km
so speed of the boat = 120 km per hour
=120 kmph