Determination of molecular formulas

Exercise 6

A non-cyclic diamide has no other function. The percentage of nitrogen is $14.0\; \%$. Find its molecular formula.

General molecular formula: $C_nH_{2n}O_2N_2$ (2 double bonds. two amine groups) $\frac{28}{12n+2n+28+ 32}$ $ = $ $0.14$ $n$ $=$ $10$ $C_{10}H_{20}O_2N_2$