I would say its option (a)
But I’m confused why you put the one-half there, since I don’t see any halves.
Steps
Six added
6 +
to twice
6 + 2()
the sum of a number and four
6 + 2(x + 4)
is equal to
6 + 2(x + 4) =
The difference of three and the number.
6 + 2(x + 4) = (3 - x)