Hi Bilyaminu,

The indices $i$ and $j$ go from 1 to 4. The first entries in each row 1, 5, 9, 13 go up by 4 so you might think of $4i$ where $i$ is the row number. But $4i$ gives 4, 8, 12, 16. Comparing these numbers to the first number in each row you see the $4i$ is too large by 3. Hence try $4i - 3.$ For $i$ from 1 to 4 this gives 1, 5, 9, 13. Hence $4i - 3$ gives the first entry in each row. How can you modify this to give the $j^{th}$ entry in each row?

Harley