Number of entries = (Number of rows) x (Number of columns) = 18

If order is (a x b) then, Number of entries = a x b

So now a x b = 18 (in this case)

Possible cases are (1 x 18), (2 x 9), (3 x 6), (6 x 3), (9 x 2), (18 x 1)

Conclusion: If a matrix has 18 elements, then possible orders are (1 x 18), (2 x 9), (3 x 6), (6 x 3), (9 x 2), (18 x 1)