Help please! Sasha did an experiment to study the solubility of two substances. She poured 100 mL of water at 20 °C into each of two beakers labeled A and B. She put 50 g of Substance A in the beaker labeled A and 50 g of Substance B in the beaker labeled B. The solution in both beakers was stirred for 1 minute. The amount of substance left undissolved in the beakers was weighed. The experiment was repeated for different temperatures of water and the observations were recorded as shown.

Experimental Observations
Substance Mass of Undissolved Substance at Different Temperatures (gram)
20 °C 40 °C 60 °C 80 °C
A 12 11 9 8
B 45 40 34 31

Part 1: Which substance has a higher solubility?
Part 2: Explain your answer for Part 1.