method use to determine empirical formula is to assume that percent given is in grams, find mole, divide by the smallest mole, and arrived at empirical formula. Then find molar mass of empirical formula and divide by g/mole given. I believe your given g/mole should be bigger as empirical is the lowest ratio structure. For example, 160.23 g/mole given.
Step 1: 74.03 g C (mol C/12.01 g C) = 6.164 mol
8.70 g H (mol H/1.01 g H) = 8.614 mol
17.27 g N (mol N/14.01 g N) = 1.233 mol
Step 2: C =6.164/1.233= 4.99 round up 5
H=8.614/1.233= 6.98 round up 7
N=1.233/1.233= 1
Step 3: C5H7N empirical formula to find molecular use given mass 160.23 g/mole/81.13 g/mole (this is MM of C5H7N)= 2
Step 4: 2 x the number of atoms C5H7N = C10H14N2 molecular formula