no no no..,

when a scalar is multiplied in a matrix, it does so with all of the rows and columns,-tis is where it differs frm deteminant wherein a scalar gets multipled with any one of the row/column.

Now coming to ur question ,firstly its incomplete --order has to be mentioned of the given matrices--which is necessary for multiplication. Since det .A=1,if we assume order of matrix A to be 3---then 3A=3 multiplied with all of rows and columns of A;--   taking 3 common we get 3*3*3 (A)

now 3AB=3*3*3*det.(A)*det(B)=81