The calculation uses the accumulated daily balance method (ADB).
We assume the statement is based on calendar month (rare!).
George owes $500 from beginning to end of June, so 30 days out of 30.
Interest accrued is 500*0.013*30/30=$6.50.
He also owes $2000 from June 12 to June 30, so 19 days inclusively.
Interest accrued is $2000*.013*(19/30)=16.47
Total interest at the end of the month=$6.50+$16.47=$22.97
574.54-396.23= 178.31
So Y=178.31
(4 x 4) - (4/4)
= 16 - 1
= 15
