The mass of a radioactive element decays at rate given by m(t) = m0e-rt, where m(t) is the mass at any time t, m0 is the initial mass, and r is the rate of decay.

Uranium-240 has a rate of decay of .0491593745. What is the mass of U-240 left after 10 hours, if the initial mass is 50 grams? [Use e = 2.71828.]