Darts - Help is lacking.

The darts problem description has a couple of problems:

a) There's a link to a wolfram alpha page for "concentric circles" that is unlikely to make much sense to most people, and even if it does, won't actually be helpful because that level of knowledge is not important to the problem anyway (I don't have a clue what the page is saying but still solved it).

b) There should be a link explaining how to calculate the distance between points. https://www.mathsisfun.com/algebra/distance-2-points.html for example is suitable for a broad audience, but there may be others.