21000.00 loan @9.5 % over 3yrs

For simple interest:

$$I = PRT$$

$$I = 21000\times{0.095}\times{3}$$

$$I = 5985.00$$ $

(note this is the interest, not the new sum)

For Compound interest:

$$A = P(1+r)^n$$

$$A = 21000\times{(1+0.095)^3}$$

$$A = 21000 \times {1.312932375}$$

$$A = 27571.58$$ $

(this is the whole new amount) 

ptr/100=(9.5%x21000x3)/100=5985/100=59.85 units is the interest