A $150-1$b drunkard $($SG$=0\mathrm{.}99)$ falls in a vat of whiskey $($SG$-0\mathrm{.}92).$ The drunkard who wishes to stay alive long enough to drink his fill of the whiskey, treads while keeping his head above. If his head up to his mouth is $15\%$ of his body volume, how much upward force must he exert by treading to keep his head out of the whiskey?