You have left a numerical subscript off of your chemical compound. KClO does not exist. You must mean KClO4 which is potassium perchlorate. In order to calculate the percentage by mass of a saturated solution, we must first look up the aqueous solubility of KClO4. This cannot be calculated, the value must simply be looked up. The aqueous solubility of KClO4 is 1.5 g per 100 mL water. Since the density of water is 1 g per mL, we know that 100 mL of water is the same as 100 g of water. So we know that 1.5 g of KClO4 in 100 g of water is a saturated solution. Since both values are in terms of mass (grams), we can divide the two and multiply by 100 to get a percentage. The percentage by mass of a saturated solution of KClO4 is 1.5/100 = 0.015 * 100 = 1.5%.