An isotope of the element erbium has a half-life of approximately 15 hours. Initially there are 23 grams of the isotope present. a. Write the exponential function that relates the amount of substance...

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Extracted text: An isotope of the element erbium has a half-life of approximately 15 hours. Initially there are 23 grams of the isotope present. a. Write the exponential function that relates the amount of substance remaining, A(t) measured in grams, as a function of t, measured in hours. A(t) = grams %3D b. Use part a. to determine the rate at which the substance is decaying after t hours. A' (t) = grams per hour c. Use part b. to determine the rate of decay at 4 hours. Round to four decimal places. A'(4) grams per hour