A circle is 360°. Since you only have 3 different types of weather, if you split the ° equally, each section would have 120°. The amount of rainy days is 10/30 or exactly 1/3, so 120° are rainy days.
If you do 30 x 12, it equals 360. So that means that each day is 12°. There were 8 cloudy days, so you can do 8 x 12 = 96°
