Applying the formula isn't that hard, but this one could be hard to write about because it depends upon the amount of time the sum is compounding or the exponen

Applying the formula isn't that hard, but this one could be hard to write about because it depends upon the amount of time the sum is compounding or the exponent in the equation. ^2 and ^3 are quite easy but when it comes to ^7/^9 there's no easy way to calculate mentally.