Find a common denominator by multiplying the two different denominators by each other to get 15. 2/3 then becomes 10/15 and 4/5 becomes 12/15.
You now have 4 and 10/15 minus negative 1 and 12/15. Subtracting a negative number results in addition, so it's 4 and 10/15 PLUS 1 and 12/15. You get 5 and 22/15, which becomes 6 and 7/15.
The answer is C.