You can see that where the graph starts at (0,15) is it's highest point, and where the graph ends (30,7) is it's lowers point. You can also just by looking at this graph see that as the line trends downwards it must have a negative slope. Also, an increase in temperature also causes an increase in kinetic energy; higher kinetic energy causes more motion in the gas, causing the gas' solubility to decrease. This means that you answer should be (B). Hope that this helps!