You deposit 6,450 in a savings account after 4 years the accountis worth 7,998 what simple interest rate did the account earn?

First subtract your end value by initial, because all we want is the amount gained from interest. 7998 - 6450 = 1548
Next, divide that by the amount of time it took to gain that money. 1548/4 =
$337 a year. 
Finally, divide your year's worth by the initial amount to get the rate in %.
337/6450 = 0.052  
OR
5.2%