Study the given pattern carefully and select the number that can replace the question mark (?) in it.

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Logic: $$\frac {\text{1st circle + lower both squares}}{3}$$ = Right circle

For, 1st 

= $$\frac {6 + 3 + 18 } {3}$$

= $$\frac {27}{3}$$

= 9

For, 2nd

= $$\frac{3 + 4 + 17} {3}$$

= $$\frac {24}{3}$$

= 8

Similarly, for 3rd

= $$\frac {5 + 13 + 15} {3}$$

= $$\frac {33}{3}$$

= 11

Thus, correct option is (a).