William and Stephanie are painting the bedrooms in their house. If he had to paint the bedrooms himself, it would take William four hours to complete the job. If Stephanie alone were to paint the bedrooms, it would take her six hours.

Working together, how long will it take William and Stephanie to paint the bedrooms?

a$.)3\mathrm{.}2$ hours

b$.)2\mathrm{.}4$ hours

c$.)1\mathrm{.}5$ hours

d$.)4\mathrm{.}5$ hours