On your way back, you spend 11 times longer on the walkway than on your way there (11 x 66 = 726).
When you walk the walkway in the opposite driving direction, you not only have to walk the length of the walkway, but in addition 11 times the distance that you saved on the way there.
Put into a formula, it looks like this:
11 x saved way + walkway length = 726
Length of saved way = walkway length - 66 (see the illustration "The way there" above)
When you enter this into the above equation, you get this result:
11 x (walkway length - 66) + walkway length = 726
11 x walkway length - 11 x 66 + walkway length = 726
12 x walkway length - 726 = 726
12 x walkway length = 1452
Walkway length = 121
Solution: You would have needed 121 steps to pass the walkway from start to end!