### Answer is 15

**How?**

Its simple, just multiply the number by 3.

**How?**

Its simple, just multiply the number by 3.

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**Explanation:**

1 + 2 => (1)^2 + (1*2) = 3

3 + 4 => (3)^2 + (3*4) = 21

5 + 6 => (5)^2 + (5*6) = 55

Thus 4 + 5 => (4)^2 + (4*5) = 36

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**How?**

If you see the rows every next number = previous number in the row +3.

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**How?**

Number on the bigger line is the multiplication of the numbers on the adjacent smaller lines, thus the answer should be 10*9=90.

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**How?**

Actually number on the right side is the square of the exact opposite number.

thus the missing number should be 6^2.

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### Answer is 10

**How?**

There is gap of 4 between numbers

8+4 = 12

3+4 = 7

9-5 = 4

simillarly

?-4 = 6=> ?=10

**NOTE:** there is a better and shorter explanation(suggested by Guestlogic in comment), opposite numbers sum is 15, that’s why answer should be 15 – 5 = 10

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Explanation: Numbers in outer circle are multiplication of the corresponding number in inner circle and 3.