The product of the above two numbers is equal to the product of the following two numbers, which is the middle number.

The product of the two numbers on the left is equal to half of the middle number, and the product of the two numbers on the right is equal to twice of the middle number.

Accordingly, the middle of the second square is 24, and the last two numbers are 3 and 8 respectively.

Just look at the numbers in the upper left corner. The four squares appear regularly as 2, 4, 6 and 8.

Just look at the numbers in the upper right corner. The four squares appear regularly as 8, 6, 4 and 2.

Just look at the numbers in the lower left corner, and four squares appear regularly, namely 4, 3, 2, 1.

Accordingly, the lower right corner of the third square is 12, the number in the middle of the fourth square is 16, and the lower right corner is 16.