Answer:
A bus takes 4.5 hours to complete a complete a journey at a speed of 40km/hr
So, in this case, We will find the distance first because the distance is constant.
distance-speed*time
distance=40*4.5
distance=180km
distance=180km
Now, we find the time to cover the distance at the speed of 45km/hr
time distance/speed
time=180/45
time=4hrs
Therefore, the answer is 4hrs
Hope it helps you.
Have a nice day!!