I don't want you to hurt yourself, but try and THINK for a few seconds:
-- Half of 10 years is 5 years.
-- Half of 6 marbles is 3 marbles.
-- Half of 2 quarts of milk is 1 quart of milk.
-- Half of 12 inches is 6 inches.
Numbers multiply and divide, but units don't.
Half of 5 km/hr is 2.5 km/hr .