Logan opened a savings account 21 years ago with a deposit of $3,471.52. the account has an interest rate of 3.1% compounded monthly. how much interest has logan earned?

P = $3,471.52, the principal
r = 3.1% = 0.031, annual ratr
n = 12, monthly compounding
t = 21 years

Note that n*t = 252.

The value after 21 years is
A = 3471.52*(1 + 0.031/12)²⁵²
   = $6,650.91

The interest earned is
6650.91 - 3471.52 = 3179.39

$3,179.39