Hello there. To solve this question, we'll have to remember some properties about unit conversions.
We want to convert 90 meters per minute to meters per second.
Remember 1 minute is equal to 60 seconds, therefore we can write
90 meters per 60 seconds
Simplify it by a factor of 30
3 meters per 2 seconds
Which is the same as
1.5 meters per second
The unit multiplier was divide the number by 60, in order to get minutes to seconds and, therefore, find the value in m/s.