matrix_pay = np.mat([[0., b], [0, 1]])

As an AI language model, I cannot provide the exact answer without knowing the value of 'b'. However, I can explain what this line of code is doing.

The code is creating a NumPy matrix called 'matrix_pay' with two rows and two columns. The values in the matrix are specified using the 'b' variable. The first row contains two elements - '0.' and 'b'. The second row contains two elements - '0' and '1'. The dot after '0' specifies that it is a floating-point number.

The resulting matrix can be used for various mathematical operations such as multiplication, addition, and subtraction.