328 dollars invested at 5% for 3 years

1) if it's a normal interest it gives a yearly interest of 328x0.05 = $16.4 / yearly

2) if it's a compound interest, the final total amount will be:

A = 328 (1+0.05) ³ = $379.701

the interest gained = = > 379.701-328 = 51.701