"A Shipment of 10 ovens has 3 defective. How many ways can a company buy 4 of these and receive A) All good units B) two good units C) at least two good units"

"Class is given 8 study problems, from which 5 will be part of upcoming exam. A student knows how to solve 6 of the problems, find probability that student can answer A) all five questions B) exactly 4 questions"

I am not sure If i have the right answers to these problems at all, and not sure how to do the last two at all.