Rotate 180 dgrees as show on delta on circle

Aright cylinder has a diameter of 8 m and a height of 6m. what is the volume of the cylinder

Can someone me with this? i’m not sure what to put for my equations.

The half-life of a certain material is 0.002 second. approximately how much of a 14-gram sample will be left after 0.004 second? a. 12 grams b. 3.5 grams c. 0.06 gram d. 7 grams