an investment of $1500 earned $35.20 at a simple-interest rate of 5.5% per year. How long was the investment held?

The formula for simple interest is I = PRT. Interest equals principle times rate times time.

$1500 is the initial investment so that would be your principle.

$32.50 is the interest that was earned so that would be the I in the equation.

5.5% is the rate, but you would need to take it out of percentage format, which means moving the decimal two places to the left because it is a percentage out of 100 (100 has two zeroes).

Your equation should look like:

32.50 = 1500*.055*T (t for time since that is what they are asking for). Then you would solve for T.