As we are given in the problem
Loan Amount = $1,600
Time =90 days
Interest rate=13%
Ordinary interest(OI) paid can be given by as
[tex] \\
\
OI=\frac{PRT}{100}, P=1600,R=13 percent, T=90days\\
\\
\
OI=\frac{1600*13*(90/365)}{100} \\
\\
\
OI=\frac{3744}{73}=\:51.287\\ [/tex]
