Suppose the charge account of Strong's Mailing Service at the local supply store had a 1.8% interest

Question:

Suppose the charge account of Strong's Mailing Service at the local supply store had a 1.8% interest rate per month on the average daily balance. Find the average daily balance if Strong's had an unpaid balance on March I of $128.50, a payment of $20 posted on March 6, and a purchase of $25.60 posted on March 20. The billing cycle ends March 31.