Two persons A and B working separately can sanitise a building in 6 and 10 hours, respectively. They work in stretches of one hour alternately. If A begins at 8 a.m., then when will the work be finished?

A

$$9\frac{1}{3}$$ h

B

$$7\frac{1}{3}$$ h

C

$$6\frac{1}{3}$$ h

D

$$8\frac{1}{3}$$ h