How much of an 800-gram sample of c14 is left after 3half-lives?

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

What kind of crystalline solid is graphite? o a. molecular solid b. metallic solid o c. network solid d. ionic solid

Biomass can be used to generate electricity. biomass relies heavily on agricultural crops. plants release carbon dioxide and water in combustion. plants use photosynthesis to originally generate the energy that is needed. the chemical energy of these plants all started with what energy source?