John has found a short-term investment opportunity. He can invest $9,000 at 0.75% interest for 21 days. How much interest will he earn on this investment if the interest is compounded daily?

P = Po*(1+r)^n

r = (0.75%/365)/100% = 2.055*10^-5 = Daily % rate expressed as a decimal.

n = 1comp./day * 21days = 21 compounding periods.

Plug the above values into the given Eq
and get:
$9,0003.88