What will be the ratio of simple interest earned by certain amount at the same rate of interest for 6 years and that for 9 years ?

A. 1 : 3
B. 1 : 4
C. 2 : 3
D. Data inadequate
Let the principal be P and rate of interest be R%. So Required ratio = [(P x R x 6/100) / (13 x R x 9/100)] = 6PR/9PR = 6/9 = 2 : 3