At what rate will $300 yield 67.50 interest in 4 years and 6 months?
Since you have not stated how often there is compounding, I will assume simple interest with no compounding.
$67.50 interest in 4.5 years is $15 per year. With a $300 investment, that is 15/300 = 5% interest
The actual interest rate is less if there is compounding, but you have not stated the compounding period.