Indira paid interest charges of $171.85 on a $4,910 invoice that was two months overdue.

What monthly rate of simple interest was she charged?

What amount paid on September 25 is equivalent to $1000 paid on the following December 1 if money can earn 7%

Payments of $700 and $1100 are due in 30 days and 210 days, respectively. If money can be invested at 7.75%, what single payment 90 days from now is equivalent to that payment stream?