Why is it "9 August until 10 September", not "9 August until 9 September"?

If it is "9 August until 10 September", the minimum balance is $996.60, isn't it?

Is it related " Debit" and "Credit"? Also please give me explanation of debit and credit.

Debit ($) Credit ($) Total($) Andrea receives a statement from the bank which gives the detail of her investment account from 1 July until 31 December, 2005. The details are as shown. Date Opening Balance: 1 July 8 August 10 September Closing Balance: 31 December 2000.00 2360.00 360.00 1363.40 996.60 996.60 How much interest has been earned on this account if the bank pays simple interest of 4.5% per annum on the minimum daily balance? Solution 1 July until 8 August = 31+8= 39 days 4.5 39 Interest = 2000 x = 9.616 100 365 9 August until 10 September = 23+ 10 = 33 days 1 The balance from 1 July until 8 August is $2000. How many days is this? 2 Determine the interest payable for this period. 3 The balance from 9 August until 10 September is $2360. How many days is this? 4 Determine the interest payable for this period. 5 The balance from 11 September until 31 December is $3723.40. How many days is this? 6 Determine the interest payable for this period. 7 Determine the total interest. 4.5 33 Interest = 2360 X = 9.602 100 365 11 September until 31 December = 20 +31+ 30+ 31 = 112 days 4.5 112 Interest = 996.60 X = 13.761 100 365 Total interest = 9.616+ 9.602+ 13.761 = 32.979 Thus the total interest eamed is $3298