Second year: (20000+m)x3.33%=n (let the interest earned in the second year be n)

Third year: (20000+n)x3.33%=p (let the interest earned in the third year be P).

So the interest earned after three years should be: m+n+p n+p.

I'll leave the specific calculation to you. Come on! Hey hey, I hope it helps you!