# How do you write a Lewis structure for CH_3NH_3^+?

And that is $6$ from the hydrogens, $5$ from the nitrogen, and $4$ from the carbon, i.e. $15$, from which subtract $1$ to account for the positive charge on the ammonium centre. We are left with $14$ electrons, or $7$ electron pairs, to distibute across the central carbon and nitrogen centres.
${H}_{3} C - {N}^{+} {H}_{3}$. Here, there are $3 \times C - H$ bonds, $1 \times C - N$ bond, and $3 \times N - H$ bonds, i.e. 7 electron pairs AS REQUIRED.
Can you do same for $C {H}_{4}$ and $N {H}_{4}^{+}$?