lineer algebra math question

Question

Reduce A and B to their triangular echelon forms U. Which variables are free and pivot ?

A=[1 2 24 6, 1 2 36 9, 0 0 12 3] B=[2 4 2, 0 4 4, 0 8 8]

Answer 1

U(A)= [1 2 0 0, 0 0 1 1/4, 0 0 0 0]

Cols 1 and 3 are pivot

Cols 2 and 4 are free

U(B) = [1 0 -1, 0 1 1, 0 0 0]

Cols 1 and 2 are pivot

Col 3 is free