unlock cell based on another cells input

I used a vlookup formula to control the content of E9 (MERGED AREA). If g12 (MERGED AREA) needs to be unlocked, the content of E9 will be "WF". All I need then is a code to unlock g12 if content of E9 is "WF". I would like it to clear g12 if the content of E9 is changed to something else other than "WF"

Here is the code that I tried but nothing seems to happen.

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Would it be easier if I didn't worry about clearing the g12 if e7 changes? If so, I could deal with that for now.

Thanks