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°
What you need to do is multiply both sides by the same number. If 8 times 6 is 48, then 7 times 6 is your answer.
If the 0 is in the numerator, the value is 0
if the 0 is in the denominator, the value is undefined
so 0/8 = 0
and 3/0 = undefined
What do we complete there is no picture