For each carbon, hydrogen and nitrogen. You have to divide each percentage by its atomic mass.
C = 53.5/12.0107 = 4.45436
H = 15.5/1.00794 = 15.377899
N= 31.1/14.0067 = 2.220365
Round the number to significant figures
C = 4.45
H =15.4
N =2.22
Divide Each Number by the smallest number out of the three
so N = 2.22/2.22 =1
H = 15.4/2.22= 6.9 =7
C = 4.45/2.22= 2
So the Formula Should Be C2H7N