The total number they were playing with must be divisible by $3$.

The number of Ben's counters must initially be divisible by $3$, Jack's by $4$ and Emma's by $5$.

It might help to work out the maximum each could have started with -
e.g. Emma could not have started with $25$ counters. Can you work out why?

How many counters could each of them have started with?

Try some possible numbers.