Answer:
if the interest is compounded annually:
$6,500 x (1 + 6%)²⁵ = $27,897
interest earned = $27,897 - $6,500 = $21,397
if the interest is compounded semiannually:
$6,500 x (1 + 3%)⁵⁰ = $28,495
interest earned = $28,495 - $6,500 = $21,995
if the interest is compounded quarterly:
$6,500 x (1 + 1.5%)¹⁰⁰ = $28,808
interest earned = $28,808 - $6,500 = $22,308