I have to graph using two different representations and the points are -10 5

Asphere has a diameter of 10 in. what is the volume of the sphere?

The weight of a radioactive isotope was 96 grams at the start of an experiment. after one hour, the weight of the isotope was half of its initial weight. after two hours, the weight of the isotope was half of its weight the previous hour. if this pattern continues, which of the following graphs represents the weight of the radioactive isotope over time? a. graph w b. graph x c. graph y d. graph z

Can someone me and explain..will award brainlest!