Total Paid: $3,633.30

Total Interest Paid: $323.30

Rule of 78's

This is kind of a misnomer, since there are 18 payments. 1+2+3+...+18 = 171

Thus, the magic number is $323.30 / 171 = $1.89

Does that get you anywhere? You weren't dividing by 78, were you?

"Unearned Interest" is that interest that would have been paid, had the loan lived to original maturity. This is trivial for the Rule of 78's...

$1.89*(1+2+3+4+5+6) = $1.89(21) = 39.69 -- Okay, a little rounding problem.

It's a little trickier for the Actuarial. Let's see what you get.