a) How many grams of potassium nitrate (KNO_3) can be dissolved in 100 mL of water at 30°C, 60°C, and 70°C?

Question

b) How many grams of potassium nitrate should be added to 100 mL of water at 25°C to make a saturated solution?

c) The solubility of potassium nitrate increases as temperature increases. When KNO_3 dissolves, is the process endothermic or exothermic?

Don't you have some solubility tables? You need some type of information to makes these calculations. Some of this information may be available in reference manuals but I'm wondering if the problem doesn't have some kind of preamble that provides this.For #3, you might put this in the form of an equation.
KNO3(s) + heat ==> KNO3(aq). Looking at the equation should answer your question.

salt