Hi guys, I have a simple question involving the collision of 2 particles of different masses. Particle 1 of mass m is travelling with speed u towards particle 2 of mass 3m which is initially at rest. I have been asked to calculate the energy loss in the impact, however in my notes there is only an example of calculating the energy loss when there is the 'special case' where the masses are the same, which is to use the formula

How would I construct the above equation given the different masses I have?

Thanks