To solve this problem, we need to find the missing number in the lower-right corner using the pattern seen in the other squares.

Let's evaluate the given pattern in each corner:

1. Top-left corner: The numbers are 9, 7, 13, and 15.

The pattern appears as follows: \((9 + 7 - 13) = 3\), then \(3 \times 5 = 15\).

1. Top-right corner: The numbers are 10, 8, 12, and 14.

Similarly, the pattern is: \((10 + 8 - 12) = 6\), then \(6 \times 2 = 14\).

1. Bottom-left corner: The numbers are 5, 3, 11, and 25.

For this pattern: \((5 + 3 - 11) = -3\), then \(-3 \times (-5) = 15\).

We see that the pattern follows \({a + b - c = x}\) and this result \(x\) multiplied by a factor results in the fourth number.

Now, applying this to the bottom-right corner:

1. The numbers are 4, 6 (missing number), 16, and 18.

Applying the pattern: \((4 + x - 16) \times n = 18\).

Let's find the solution by setting \(n\) consistent through other corners:

• Calculating for \(x\):

Solve \((4 + x - 16) \times 1 = 18\), we get: \({4 + x - 16 = 18}\), implying \(x = 6\).

Therefore, the missing number is 6.

Hence, the correct answer is 6.