A half note has a duration of 2 beats. An eighth note rest represents half a beat. To find out how many eighth note rests are needed to equal the duration of a half note, you can divide the duration of the half note by the duration of the eighth note rest:
2 beats (for a half note) รท 0.5 beats (for an eighth note rest) = 4 eighth note rests.
So, the answer is 4 eighth note rests.