Please help Know how to read and calculate speed from a motion Graph

If you mix chlorine lithium in nickel together which two elements would be the most reactive

Ben(55 kg) is standing on very slippery ice when junior(25kg) bumps into him. junior was moving at a speed of 8m/s before the collision and ben and junior embrace after the collision. find the speed of ben and junior as they move across the ice after the collision .

How to calculate voltage drop in a series circuit