Joyce took out a loan for $ 21,900 at 12 percent on March 18, 2007. Which will be due on Jan 9, 2008. Use ordinary interest, Joyce will pay back on Jan 9 a total amount.

To calculate the total amount that Joyce will pay back on January 9, 2008, we need to first calculate the interest accrued on the loan over the duration.

The formula to calculate simple interest is:

Interest = Principal × Rate × Time

Where:
Principal = $21,900
Rate = 12% (or 0.12 in decimal form)
Time = Total number of days between March 18, 2007, and January 9, 2008

Next, we calculate the number of days between the two dates.

March 18 to December 31, 2007 = 288 days
January 1 to January 9, 2008 = 9 days

Total days = 288 + 9 = 297 days

Now we can calculate the interest:

Interest = $21,900 × 0.12 × (297/365)

To find the total amount that Joyce will pay back on January 9, 2008, we add the interest accrued to the principal amount:

Total amount = Principal + Interest

Total amount = $21,900 + (Interest calculation)

By plugging in the values and calculating the expression, we can find the total amount.