Read the sentence.
i spend about half my time, he spends two thirds of his time, and she spends a quarter, or maybe a third, of her time on research. where in the sentence should the writer add a hyphen? i spend about-half my time, he spends two thirds of his time, and she spends a quarter, or maybe a third, of her time on research. i spend about half my time, he spends two-thirds of his time, and she spends a quarter, or maybe a third, of her time on research. i spend about half my time, he spends two thirds of his time, and she spends a quarter, or maybe a-third, of her time on research. i spend about half my time, he spends two thirds of his time, and she spends a quarter, or maybe-a-third, of her time on research.
where in the sentence should the writer add a hyphen?