The numbers in each set are related to each other in a certain way.
(6, 64, 2), (8, 225, 7), (3, ?, 9)

Based on the relationship among the numbers in the first two sets, select the number that can replace the question mark (?) in the third set.

Let's identify the mathematical relationship between the numbers in each triad (1
st
 number,2
nd
 number,3
rd
 number):

Set 1: (6, 64, 2)
Notice that 64 is a perfect square: 64=8
2
.
How can we get 8 from 6 and 2?

6+2=8⟹8
2
=64
Set 2: (8, 225, 7)
Notice that 225 is a perfect square: 225=15
2
.
How can we get 15 from 8 and 7?

8+7=15⟹15
2
=225
Logic: (First number+Third number)
2
=Second number

Set 3: (3, ?, 9)
Applying the same rule:

Second number=(3+9)
2
=12
2
=144
Therefore, the missing number is 144.