Final answer:
Matrix a is given and it is equal to matrix b. However, without the values of matrix b, we cannot determine its value.
Step-by-step explanation:
The given matrix a is:
a = [2 0 -9 11]
[18 -7 0 21]
If matrix a is equal to matrix b, then we need to find the value of matrix b.
Since the question only provides information about matrix a, we cannot determine the value of matrix b without additional information. We need the matrix b to solve for its values.