Number of worker (W) required to finish a fixed work is inversely proportional to the time ( T) taken .

In first case number of worker is 15 and time taken is 48 hrs.

In second case number of worker is unknown (let it be x) and the time given is 30 hrs

So x/15=48/30

=x= 48/30*15=24

Hence number of workers required is 24