input: Write a python function to multiply two matrices.
  assert multiply_matrices([[1, 2], [3, 4]], [[5, 6], [7, 8]]) == [[19, 22], [43, 50]]
  assert multiply_matrices([[1, 0, 2], [-1, 3, 1]], [[3, 1], [2, 1], [1, 0]]) == [[5, 1], [4, 2]]
  assert multiply_matrices([[2, 4], [6, 8]], [[1, 3], [5, 7]]) == [[22, 34], [46, 70]]
output: def multiply_matrices(A, B):
      result = [[0 for _ in range(len(B[0]))] for _ in range(len(A))]
      for i in range(len(A)):
          for j in range(len(B[0])):
              for k in range(len(B)):
                  result[i][j] += A[i][k] * B[k][j]
      return result