HELP: quarks, protons, neutrons, physics

Protons have 2 up quarks, 1 down quarks (UP, UP, DOWN)
Neutrons have 1 up quark and 2 down quarks (DOWN, DOWN, UP)

With the above information, the charge on each quark is found, and also a correct prediction on the charge of a hypothetical particle consisting of 3 up-quarks (UP, UP, UP).

QUESTION: Duplicate his results (e is the magnitude of the charge on the electron). Please provide full solution.