Hi Kathy.
Let me make sure I am reading your equation correctly.
2/3 + 1/3(1/4f-4/3)
distributing the 1/3 through the second term.
2/3 + 1/12f-4/9
Now combine the two constant terms.
2/3 - 4/9 + 1/12 f
6/9 - 4/9 + 1/12 f
2/9 + 1/12 f