Find the indicated probability?

A)The quiz consists of 10 true/false questions. To pass the quiz Judy must answer at least 7 questions correctly. But if Judy guesses on each question, what is the probability that she will pass the quiz?

B)The multiple choice exam has 10 questions each of which has 4 possible answers, only one of which is correct. If Judy, who forgot to study for the exam, guesses on all questions, what is the probability

that she will answer exactly 3 questions correctly?

So I remember the answer for the first part being .172 but need help knowing how to get that answer. iTS followup question only confuses me more. (Headbang)

Help would truly be appreciated...