Can you help me with this two question? just multiple choice but need a reason why we choose those answer

Question 4: Suppose that the following two processes/threads are run on a single-CPU system. The code below is informal, but the meaning of all statements is clear. The semantics of test_and_set is as defined in class. What is the value of sum printed by P2 before the thread terminates? a. 0 b. 2 c. 4 d. 6 e. 8 f. 10 g. 12 h. 14