To solve this type of problem, first determine the number of moles of copper produced.
moles = mass/elemental mass = 6.35/63.5 = 0.1 moles
Now write the reaction taking place, and assume you have a copper +2 ion in solution.
Cu^+2 + 2 e^-1 = Cu
This means that it takes two moles of electrons for every mole of copper that has been reduced.
Since you produced 0.1 moles of copper, you had to use 0.2 moles of electrons.