Problem: Suppose the charge account of Strong's Mailing Service at the local supply store had a 18% interest rate per month on the average daily balance. Find the average daily balance if Strong's had an unpaid balance on March 1 of $171.60, a payment of$10 posted on March 11, and a purchase of $29.70 posted on March 16. The billing cycle ends March 31.
The average daily balance is??