How many nuclei of u remain in a rock if the activity registers 280 decays per second(note that the half life of uranium-238 is 4.468x10 years)

The magnitude of the poynting vector of a planar electromagnetic wave has an average value of 0.939 w/m^2 . the wave is incident upon a rectangular area, 1.5 m by 2.0 m, at right angles. how much total electromagnetic energy falls on the area during 1.0 minute?