I'm not to sure what the question is but it sounds like you are describing the Law of Conservation of Energy: stating that energy can't be created nor destroyed, but instead transferred or conserved.
Answer:
This looks like an example of combustion
Explanation:
lily's speed would be twice john's speed
q = 40 C
e = 1.6×10^-19 C
n = ?
n = q/e
n = 40/1.6×10^-19 C
= 2.6×10^20