How much of the circle is clear ? 1/2 of it and 1/9 of it.
How much of it is (1/2 + 1/9) ?
Before you can add fractions, they need to have the same denominator.
The least common multiple of 2 and 9 is 18, so that's a good choice.
1/2 = 9/18
1/9 = 2/18
(1/2 + 1/9) = (9/18 + 2/18) = 11/18 . That's how much of the circle is NOT shaded.
Since 11/18 of it is NOT shaded, the remaining 7/18 of it is shaded.