Why does the narrator in sorrentino's “there’s a man in the habit of hitting me on the head with an umbrella” refuse to take the man with the umbrella to the police station

This can be answered using the compound interest formula, which is as follows:

F = P (1 + r/n)^nt
Where:
F = future value
P = Principal value
r = yearly interest rate
n = interest period
t = duration in years

Substituting the given values:

F = 120(1 + 0.3/12)^12(5)
F = 527.97

Since the value being asked is the interest to be paid, the future value is to be subtracted by the principal value to obtain the interest. This will be:

interest = F - P
interest = 527.97 - 120
interest = 407.97

Therefore, Bill should ask Sam to pay $407.97 as interest for the cash advance.