How do I approach this question?

Problem Description
You are given a 3 × 3 grid which contains integers. Some of the 9 elements in the grid will have a value already, and the remaining elements will be unspecified. Your task is to determine values for the unspecified elements such that each row, when read from left-to-right is an arithmetic sequence, and that each column, when read from the top-down, is an arithmetic sequence.

Recall that an arithmetic sequence of length three is a sequence of integers of the form a,a+d,a+2d

for integer values of a and d. Note that d may be any integer, including zero or a negative integer.

Sample Input 1

8 9 10
16 X 20
24 X 30

Output for Sample Input 1

8 9 10
16 18 20
24 27 30

Sample Input 2

14 X X
X X 18
X 16 X

Possible Output for Sample Input 2

14 20 26
18 18 18
22 16 10

For the first sample input I understand how I could make a program to solve it, but I am unsure about the second one.