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In brief, this is what you do. Let me know where you need additional help but show your work from the beginning to the point you need help.
You need to convert 0.48g CO2 to g C.
Convert 0.1636g H2O to g H (not H2).
Convert 0.0618g NH3 to g N (not N2).
a. gC + gH + gN = 0.2 would prove nothing else was there except C,H,N.
b. Then convert g C, H, N, to mols and from there the empirical formula.