Number of entries = (Number of rows) x (Number of columns) = 7

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

So now a x b = 7 (in this case)

Possible cases are (1 x 7), (7 x 1)

Conclusion: If a matrix has 18 elements, then possible orders are (1 x 7), (7 x 1)