Have you been taught how to solve simultaneous linear equations?
Then, write atom balances. Say, in 2nd example for Cu, H, N, O.
4 linear eq. in 6 unknowns. Solve.
Matrix based solving might speed up the process.
It isn't the way Chem. classes typically teach but I find it neater. If you're lucky maybe your Scientific Calculator will have a linear eq. solving function too.