Final answer:
Using the simple interest formula, Coral would need 8 years for her $500 investment at a 5.5% annual rate to grow to $720, which doesn't match any of the provided answer choices. There might be a mistake in the question or choices provided.
Step-by-step explanation:
In order to calculate the time it will take for Coral to have $720 in her account with simple interest, we need to use the formula for simple interest:
Interest = Principal × Rate × Time
Let's denote the principal amount as P, the annual interest rate as r, and the time in years as t. Here, P=$500, r=5.5%, and we are solving for t. Since simple interest is calculated annually, t will be the number of years.
Coral wants her $500 investment to grow to $720. The total interest earned will be $720 - $500 = $220. Plugging in her interest rate (expressed as a decimal) we get:
$220 = $500 × 0.055 × t
This simplifies to:
220 = 27.5t
Dividing both sides by 27.5 gives us:
t = 8 years
However, since the available answer choices do not include 8 years, there seems to be a mistake. If the student or the given question meant compound interest, then the calculation would be different, involving the compound interest formula and possibly matching one of the given choices. But with simple interest as stated in the question, the correct time frame for Coral's investment to reach $720 is not available in options A) 4 years B) 5 years C) 6 years D) 7 years.