A certain sum of money amounts to Rs. 678 in 2 years and to Rs. 736.50 in `3 1/2` years. The rate of interests is:

Explanation

`A=P(1+(RT)/100)`

`678=P(1+(R*2)/100)-(1)`

`736.5=P(1+(R*(7/2))/100)-(2)`

dividing equation 1 and 2

`678/736.5=(1+(2R)/100)/(1+(R)/100)`

solving this

R=6.5%

option B is correct.