At 70% off, the rope length is x/3, x/3-y = 4................①.
At 40% off, the rope length is x/4, x/4-y =- 1...........②.
X/3-X/4 of ①-② = 5.
What about up there? Answer b is right.
In fact, I think
At the 30% discount, there are three strands of rope, x/3 for each length, 4 feet more and 4 feet more. x/3-y=4×3................①
At a 40% discount, there are four strands of rope, each strand is x/4, less 1 foot, and each strand is less 1 foot. x/4-y=- 1×4...........②
I don't want your points, I just want to solve the problem.