$(20$pts$)$A $400-$gram aluminum block at $120C$ is placed into a container holding an unknown amount of water at $5C.$ The block$/$water are thermally isolated from the outside environment and are allowed to come to thermal equilibrium. The equilibrium temperature is then measured to be $15C.$ Given that the specific heat capacities of aluminum and water are $900\frac{J}{k}\frac{g}{}C$ and $4186\frac{J}{k}\frac{g}{}C,$ respectively:

a$.$ Determine how much water is in the container $($Express your answer in $mL)$

b$.$ What would be the equilibrium temperature of the system if the container held twice the amount of water as found in part a$?($In other words, a $400-$gram block of aluminum at $120C$ is added to twice the amount of water at $5C)$