Find the volume of the solid of revolution formed by rotating about the x--axis the region bounded by the given curves.
f(x)=2ex, y=0, x=-2, x=1.

The half-life of a certain material is 0.004 second. approximately how much of a 20-gram sample will be left after 0.016 second? a. 5 grams b. 16 grams c. 0.32 gram d. 1.25 grams