Loren loaned his brother $3,000. In 4 years his brother paid back $3,000 plus $660 in interest. What was the interest rate?

1. Use the simple interest formula I equals P times r times t. 2. Substitute the known values: 660 equals 3,000 times r times 4, which simplifies to 660 equals 12,000 times r. 3. Divide both sides by 12,000 to get r equals 0.055. 4. Converting 0.055 to percent form gives a rate of interest of 5.5%. _Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 3 "Math Models", section 3.2 Solve Percent Applications_