After 5 years, a $2,450 investment is worth $3,123.75 What is the simple annual interest rate for this investment?

Simple interest is just i=prt, where i=interest, p=principle, r=rate, t=time

And that simple interest will be the difference between the final value and the initial value so:

3123.75-2450=2450r*5

673.75=12250r

0.055=r

So the annual simple interest rate (as a percentage) is 100 (.055) = 5.5%