Salt is sodium chloride.
sodium atomic weight 23 chlorine atomic weight 35.45
so sodium makes up 23/(23+35.45) the weight of salt = 23/58.45
If he can only have 1600 mg of SALT per day, that is only 23/58.45 x 1600 = 629.6 mg sodium per day
In one week that would be 629.6 x 7 = 4407 mg sodium per week.