switching losses
well in truth,
you just do by intuition.
draw out your I & V waveforms at switch on and switch off....
approximate using straight/slanted lines...........then you get triangles............
find the energy in a triangle by integral of V * i(t) over time.
VIt/t = power loss
then just add 'em up since they happen every time it switches.
please do not look for the formula-from-heaven as you will spend the rest of your life looking for it next time.
otherwise, just say its 30% of on-state losses for each fet