Element X is a radioactive isotope such that every 61 years, its mass decreases by half. Given that the initial mass of a sample of Element X is 9400 grams,
write a function showing the mass of the sample remaining after t years,
where the annual decay rate can be found from a constant in the function.
Round all coefficients in the function to four decimal places. Also, determine
the percentage rate of decay per year, to the nearest hundredth of a percent.