Find all possible orders of matrices having 7 elements.

Number of entries $=$ (Number of rows) $\times$ (Number of columns) $=7$

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

So now $\mathrm{a} \times \mathrm{b}=7$ (in this case)

Possible cases are $(1 \times 7),(7 \times 1)$

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