correct answer is: b) 12%

Explanation

Here, A sum of money means ‘Principal’ .
Let, Principal = ₹ x
\therefore Amount =\left(x\times\frac{8}{5}\right) or ₹\frac{8x}5
We know,
S.I. =\left(amount\ -\ principle\right)
\rightarrow S.I. =\left(\frac{8x}{5}\ -\ x\right) or \left(\frac{8x\ -\ 5x}{5}\right) or ₹\frac{3x}5
And Time = 5 years
\therefore The rate of interest is =\ \frac{100\times S.I}{P\times T}
\rightarrow Rate =\frac{100\times3x}{x\times5\times5} %
\therefore Rate = 12 %
Ans: The rate of interest 12 %.