### 2.42.18 Multiply a row by an expression : `mRow`

`mRow` takes three arguments : an expression, a matrix *A* and an
integer *n*.

`mRow` returns the matrix obtained by replacing in *A*, the row of index
*n* by the product of the row of index *n* by the expression.

Input :

`mRow(12,[[1,2],[3,4]],1)`

Output :

`[[1,2],[36,48]]`