A sum of money amounts to Rs. 9800 after 5 years and Rs. 12005 after 8 years at the same rate of simple interest. The rate of interest per annum is:

A. 5%
B. 8%
C. 12%
D. 15%

S.I. for 3 years = Rs. (12005 – 9800) = Rs. 2205.
S.I. for 5 years = Rs.[ (2205/3) x 5 ] = Rs.3675

Principle = Rs.(9800-3675) = Rs.6125

Rate=12%