Cu + HNO3 --> Cu(NO3)2 + NO + H2O
how to balance... WILL GIVE 15 POINTS

3 Cu + 8 HNO3 --> 3 Cu(NO3)2 + 2 NO + 4 H2O

Explanation:

Make sure both sides are equal

3 Cu + 8 HNO3 --> 3 Cu(NO3)2 + 2 NO + 4 H2O

// start by those elements that change their oxidation degree

Cu and N

// also you can write reduction-oxidation reactions

+ 2 --> | 2

- 3 -->   | 3

// write the numbers of electrons that are lost/gained as the coefficients of the opposite elements

// then check if H and O are the same on both sides

// adjust if they aren't.

c. 75.7

i think that is the right