A sample of an unknown chemical element naturally loses its mass over time. The relationship between the elapsed time ttt, in months, since the mass of the sample was initially measured, and its mass, M(t)M(t)M, left parenthesis, t, right parenthesis, in grams, is modeled by the following function: M(t)=120⋅(81625)t Complete the following sentence about the rate of change in the mass of the sample. Round your answer to two decimal places.