What annual interest rate is needed for a principal of $3000 to grow to $5500 in 3 years if the interest is computed as simple interest?

Question

I DONT KNOW HOW TO SET THIS PROBLEM UP, I KEEP GETTING THE WRONG ANSWER AND CANT FIGURE OUT THE RIGHT ONE. 

Answer 1

the underlying formula that you want to use on this one is

R = I / (PT)

for this scenario that means taking

R = (5500 - 3000) / (3000 * 3)

R = 2500 / 9000

R = 0.2778 * 100% = 27.78%

meaning that an annual interest rate of 27.78% is needed