
Simple intrest problem
"Suppose that you take out an unsubsidized Stafford loan on Sept 1 before your junior year for $5500 and plan to begin paying it back on Dec 1 after graduation and grace period 27 months later. The interest rate is 6.8%. How much will you owe then, and how much of that will be in interest?"
The formula is I=Prt.

This shouldn't be too difficult.
The total amount owing will be $\displaystyle P+I$
The interest as you have shown is $\displaystyle I = Prt = 5500\times \frac{6.8}{100}\times t$
Here's the tricky bit, what is $\displaystyle t$ in years?