It wants 1/2 of the already shaded part to be erased. From looking at it, I'd say that 2/3 of the shape is shaded. It wants 1/2 erased, and 1/2 of 2/3 is 1/3. Then you'd subtract that 1/3 from 2/3 to get 1/3, so therefore the answer is 1/3.
