To multiply a matrix by a constant, simply multiply every element within the matrix by that constant. Therefore, in the example provided, multiply each individual entry by 4 to receive your answer.
Multiplying a matrix #A# by a single number, called a scalar, is a fairly straightforward process when compared with multiplying two matrices together. One can choose to represent the scalar as a matrix if one wishes, by using the identity matrix (which serves as the multiplicative identity for matrices) and changing every entry on the main diagonal from 1 to the scalar (in this case 4). This is not usually required; however, it may provide assistance in conceptualizing why scalars work in this manner.