For getting to the actual value of "x", we have to solve an equation.
(5x - 1/2 = 12
5x -1 = 12 * 2
5x - 1 = 24
5x = 24 + 1
5x = 25
x = 25/5
= 5
From the above deduction we can easily conclude that the value of "x" is 5 and the correct option among all the options that are given in the question is the second option or option "B". I hope the procedure is clear enough for you to understand.