Average balance=total number of dollar-days / total number of days
Total number of dollar days
= 12010+15012+90*8
=1200+1800+720
=3720 dollar-days
Total number of days
= 10 + 12 + 8
=30 days
Average daily balance
= Dollar-Days / Days
= 3720 dollar days / 30 days
= 124 dollars
