Element X is a radioactive isotope such that every 91 years, its mass decreases by half. Given that the initial mass of a sample of Element X is 80 grams, how long would it be until the mass of the sample reached 68 grams, to the nearest tenth of a year?

Suppose that the price p, in dollars, and the number of sales, x, of a certain item follow the equation 4 p plus 4 x plus 2 pxequals56. suppose also that p and x are both functions of time, measured in days. find the rate at which x is changing when xequals2, pequals6, and startfraction dp over dt endfraction equals1.5.