To get maximum current through a resistance of $2.5\Omega$, one can use $‘m’ $ rows of cells, each containing $‘n’$ cells connected in series. The internal resistance of each cell is $0.5\Omega$. What are the values of $ n$ and $m$ if the total numbers of cells are $45$?

Question

$\begin {array} {1 1} (a)\;3,15 & \quad (b)\;5,9 \\ (c)\;9,5 & \quad (d)\;15,3 \end {array}$