A laboratory test tank contains seawater of salinity S and density ρ. Water enters the tank at conditions (S1,ρ1,A1,V1) and is assumed to mix immediately in the tank. Tank water leaves through an outlet A2 at velocity V2. If salt is a "conservative" property (neither created nor destroyed), use the Reynolds transport theorem to find an expression for the rate of change of salt mass Msalt within the tank.