Apply the problem-solving strategy to find the rate of simple interest given the principal, interest earned, and time.

Problem: Hang borrowed $\$7{,}500$ from her parents to pay her tuition. In $5$ years, she paid them $\$1{,}500$ interest in addition to the $\$7{,}500$ she borrowed. What was the rate of simple interest?

1. Read the problem carefully.
2. Identify what to find: the rate of simple interest.
3. Name the unknown: Let $r$ = rate of interest.
4. Translate into an equation using the simple interest formula $I = Prt$. Given $I = 1{,}500$, $P = 7{,}500$, and $t = 5$: $1{,}500 = (7{,}500)r(5)$
5. Solve the equation: Multiply $7{,}500$ and $5$: $1{,}500 = 37{,}500r$ Divide both sides by $37{,}500$: $0.04 = r$ Change the decimal to percent form: $4\% = r$
6. Check the result: $I = Prt$ $1{,}500 \stackrel{?}{=} (7{,}500)(0.04)(5)$ $1{,}500 = 1{,}500 \checkmark$
7. Answer: The rate of interest was $4\%$.