he three numbers in each group are related in the same way.Choose the number that completes the last group.( 18 [ 15 ] 12 )( 13 [ 12 ] 11 )( 9 [ ? ] 15 )A11B12C6D15E24

The pattern in the groups seems to be that the number in the brackets is 3 less than the first number and 1 less than the last number.

In the first group, 18 - 3 = 15 and 12 + 1 = 13. In the second group, 13 - 1 = 12 and 11 + 1 = 12.

So, applying this pattern to the third group, we need to find a number that is 3 less than 9 and 1 less than 15.

9 - 3 = 6 and 15 - 1 = 14.

Since 6 is not equal to 14, this pattern does not apply.

So, let's try another pattern.

In the first group, 18 - 15 = 3 and 15 - 12 = 3. In the second group, 13 - 12 = 1 and 12 - 11 = 1.

So, the difference between the first and second numbers and the second and third numbers is the same.

Applying this pattern to the third group, we need to find a number that when subtracted from 9 gives the same result as when 15 is subtracted from it.

Let's call this number x.

So, 9 - x = x - 15.

Solving this equation for x gives x = 12.

So, the answer is B12.