Question 18
An arithmetic sequence is a sequence in which each term after the first is obtained by adding a constant to the previous term. For example, $2,$ $5,$ $8,$ $11,$ $14$ is an arithmetic sequence with five terms, in which the first term is $2$ and the constant $3$ is added. Each row and each column in this $5\times5$ array is an arithmetic sequence with five terms. What is the value of $X?$
