We have a circle, where a fraction is shaded.
The not-shaded fraction is the sum of 4/9 and 1/2. These fraction represent the fraction of the circle area (you can see it clearly with "one half" fraction).
Then, if we substract from 1, the complete circle, the not shaded parts (4/9+1/2), we should get the shaded fraction:
The shaded part represents 1/18 of the circle.