Answer:
At a rate of 5%.
Explanation:
This is a simple interest problem.
The simple interest formula is given by:

In which E is the amount of interest earned, P is the principal(the initial amount of money), I is the interest rate(yearly, as a decimal) and t is the time.
In this question:
Payment plan for $1500 means that

$450 interest after 6 years means that

We have to find the rate I. So




At a rate of 5%.