Find the principal (original) amount if $675 "ordinary" interest accrues after 6 months.
Depending on your definition of "ordinary" interest as being simple interest:
P = ? (the unknown)
rate (`r` ) = 0.09 (or `9/100` ) /
time period (`t` )= 6 months which is 0.5 of a year /
interest accrued (`I` ) = $675
We know that `I = P times r times t`
Substitute what you know into the formula:
$675 = `P` `times 0.09 times 0.5`
Now solve for `P`
`675 = P times 0.045 `
`therefore 675/0.045 = P`
`therefore P = $15000`
There is another definition of "ordinary" interest being based on a 30-day month (= 360 days in a year), in which case a standard 6 months (ie of 365 days) becomes 0.50694 of a year of 360 days instead of 0.5 of a standard year.
Answer based on a standard calculation of simple interest = `$15000`