# A tank contains $200\; gal$ of water of $40\; lb$ salt dissolves. $5\; gal$ of brine , each containing $2\; lb$ of dissolved salt, run into tank per minute and mixture kept uniform by stirring runs out at same rate. Find amount of salt $y(t)$ in tank at any time $(t)$
$(a)\;y(t)=300-360\;e^{-0.05t} \\ (b)\;y(t)=360-300 e^{-0.05t} \\ (c)\;y(t) =400 -360 e^{-0.025t} \\ (d)\;y(t)=360-400 e^{-0.025t}$