How to calculate the audit fee u should pay

Natural log audit fee = 1.906 (cash flow / total assets) + (0.612 x Big 4 [zero if not Big 4]) + 0.382 (natural log of total assets) - 0.219 (quick ratio) - 0.004 (return on equity)

Then Exponent (Natural log audit fee) = audit fee u should pay = PREDICTED AUDIT FEE
then
ACTUAL AUDIT FEE - PREDICTED AUDIT FEE = OVER OR UNDER PAYMENT OF AUDIT FEE