For a particular collision, she detects the emitted products and find 15 protons, 2 antiprotons, 7 positrons, and 24 neutral particles. How many electrons are also emitted

First of all, there were a total charge of + 13e (6 protons from carbon and 7 protons from nitrogen), that meant there requires to be a total charge of + 13e after the collision occurred. Listed is 16 protons (+16e), 3 antiprotons (-3e), 8 positrons (+8e) and 16 neutral particles (0e), so the total charge listed is + 21e, meaning an excess of + 8e, meaning you need 8 electrons (-8e) to balance out the charge.