According to the rules of operations, do multiplications and divisions (from left to right) before you do additions and subtractions (from left to right)
30/2 - 5·2 + 2
(Do 30/2 = 15 first.)
15 - 5·2 + 2
(Do 5·2 = 10 next.)
15 - 10 + 2
(Now, do 15 - 10 = 5.)
5 + 2
= 7