Question 27
In the $3\times3$ grid below, each box is occupied by the numbers $1,2,3,4,5,6,7,8,9$ respectively, such that any two consecutive numbers must be arranged in adjacent boxes, i.e. 1 and 2 are adjacent, 2 and 3 are adjacent, ..., 8 and 9 are adjacent. Given that the sum of $a$ and $b$, as shown in the diagram, is equal to 12, find the value of $x$.
