3.0e+02 is 300 g of water. a) KCl solubility at 30C shown as 35 g of salt per 100 g of water. So in 300 g of water you can dissolve at most 35*3=105 g of KCl. b) KClO3 solubility at 30C is 10g of salt per 100g of water. To form saturated solution with 300 g of water you will need 10*3=30 g of KCl. I suppose program allows for some errors and that is the explanation why 25 g is also a correct answer. But in general this is strange. c) Pb(NO3)2 solubility is shown as 65 g of salt per 100 g of water at 30C. Thus you should use 65*3=195g of this salt to make saturated solution.