6. As we can see from the graph, if we have only 100 grams of water, at 30°C, we will have 10 grams of KClO3 being dissolved in water, therefore if we have 300 grams of H2O, we will have 30 grams of KClO3 being dissolved at 30°C
7. The least soluble substance will be the one that shows up first in the temperature "line", if you follow the temperature up, the first solute that is listed will be considered to least soluble, therefore the least one will be KClO3