Add k times a row to an another row : mRowAdd

mRowAdd takes four arguments : a real k, a matrix A and two integers n1 and n2.
mRowAdd returns the matrix obtained by replacing in A, the row of index n2 by the sum of the row of index n2 and k times the row of index n1.
Input :

mRowAdd(1.1,[[5,7],[3,4],[1,2]],1,2)

Output :

[[5,7],[3,4],[4.3,6.4]]