Description for Correct answer:
The required difference in amount and principal is SI = A - P.

Here, P = RS. 4000, R = 5%, T = 4 yr

According to the formula,

SI = \( \Large \frac{P\times R\times T}{100} \)

= \( \Large \frac{4000\times 5\times 4}{100} \) =RS.800