1) The partial pressure?

The first part is unanswerable, as we have no notion of the units involved in the pressure. The second one is done as follows: the total number of moles of solute are 0.003 x 0.353, which is 1.059 millimoles, but each molecule contains four ions, so the total number is four times that, or 4.236 millimoles -- matching the book answer.