How do you solve these types of questions?

Acircle has a diameter will endpoints of (-2,8) and (6, 4). what is the center of the circle

Me! last question, and i'm stuck! write the algebraic expression that models the word phrase. the product of 2 divided by the number h and 8 more than the number k

If a suspect is in possession of 20 grams of cocaine how many ounces does he possess what will the charge be