The rate at which a solid substance dissolves

varies directly as the amount of undissolved solid present in

the solvent and the difference between the saturation

concentration of the substance and the instantaneous

concentration of the solution. Five grams of A are placed in

$100$ cc of solvent B$.$ The solution when saturated will hold $10$

grams of A$.$ If two grams of A dissolves in $1$ hour, how many

grams of A will be in solution is $2$ hours?