Floating boat

Classical Mechanics Level 2

Two boats $A$ and $B,$ connected with a string, are floating on a calm lake. The mass of $A$ and $B$ are $100 \text{ kg}$ and $150 \text{ kg},$ respectively, and the distance between them is $25 \text{ m}.$ If the string is pulled from boat $A$ with a constant force and the two boats meet in $20 \text{ seconds},$ what is the distance that boat A moves?

Suppose that there is no friction whatsoever.