If both A-1 and the LU factorization of an n n matrix A have already been

Question:

If both A-1 and the LU factorization of an n × n matrix A have already been computed, then it is more efficient to solve a system Ax = b by multiplying A-1b rather than solving LUx = In the case of a true statement, explain or prove your answer. In the case of a false statement, give an example to show that the statement is not always true.
b using forward and back substitution.