The chemical element einsteinium -253 naturally loses its mass over time . A sample of einsteinium-253 had an initial mass of 320 grams when we measured it. The relationship between the elapsed t, in days, and the mass,m(t), in grams left in the sample is modeled by the following function: M(t)=320•(0.125)^t/61.4 complete the sentence: the sample loses 87.5% of its mass every ___ days.