The question being begged is: 'How do you solve this problem explicitly for x'.
Changing the subject of a formula basically means that if you have a formula in the form: then the 'subject' of the formula is 'y'. Changing the subject to 'x' would yield: .
So in your problem we have: and we want to make 'x' the subject of the formula.
Let's start by getting rid of those parentheses:
Now let's solve for 'x':