If rate of interest and time on a certain bill are numerically

If rate of interest and time on a certain bill are numerically equal and true discount is 81 times of banker's gain, find the rate of interest ?

Given that, n = 81
According to the formula.
R = 10√1/n%
= 10√1/81%
= 10 x (1/9) % = 1¹/_{9_%}