Find the point that matters most

You will remove each point of a data set in turn, work out $r$ without it, and find the point whose removal changes $r$ the most. The checker uses the heights and arm spans of the lesson, with the typing mistake.

The idea. A point with a large pull on $r$ changes $r$ a lot when it is left out. Comparing $r$ with and without each point is a simple way to find such a point.

Your tasks.

1. Finish without(values, i). Return a new list with item i left out.
2. Finish change_in_r(xs, ys, i). Return the size of the change in $r$ when point i is left out.
3. Finish most_important(xs, ys). Return the index of the point with the largest change.