One. If Ca had a 2 (or more) before it or a small 2 (or more) after it towards the bottom, then there would be more than 1. Since there are no numbers before or after Ca, there is only one Ca atom.
Well, Ca has an atomic mass of 40, so one mole of Ca (6.022x1023 atoms) equals 40g.
To get 5kg of Ca, you would times the 40g (one mole) by 125.
5kg of Ca has 125x(6.022x1023),...