Calculate the commercial interest of
a) $3,100 for 125 days at 9% semi-annually
b) $2,500 from September 8 to February 12 of the following year at 4% quarterly
c) $6,640 for 9 business months and 25 days at 3.1% bi-monthly
d) $ 1,600 from January 13 to October 20 of the same leap year at 0.94% per month
e) $ 4,000 for 8 months at 0.88% monthly
f) $1,350 for 2 months at 18% yearly