Explanation:

Simple Interest = Rs. 80

Rate of interest =$\dfrac{100 \times SI}{PT} = \dfrac{100 \times 80}{100 \times 8} $= 10per annum

Now lets find out the compound interest of Rs. 14,000 after 3 years at 10%

P = Rs.14000

T = 3 years

R = 10%

Amount after 3 years = P$\left(1 + \dfrac{R}{100}\right)^T$ = 14000$\left(1 + \dfrac{10}{100}\right)^3$

= $14000\left(\dfrac{110}{100}\right)^3 = 14000\left(\dfrac{11}{10}\right)^3 = 14 \times 11^3 = 18634$

Compound Interest = Rs.18634 - Rs.14000 = Rs.4634