Recap - Air Track

On a level air track, glider A ($0.3\ \mathrm{kg}$) starts at rest, and a string pulls it to the right with a net force of $0.6\ \mathrm{N}$ for $0.5\ \mathrm{s}$. It then coasts into glider B ($0.2\ \mathrm{kg}$), which slides toward it at $0.5\ \mathrm{m/s}$, and they stick together. Taking right as positive, find the velocity $\relax v_{f}$ of the joined gliders.