### 5.45.18 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]]