This challenge will help you interpret mathematical relationships both algebraically and geometrically.

Create a function that takes a number (step) as an argument and returns the number of matchsticks in that step. See step 1, 2 and 3 in the image above.
match_houses(1) ➞ 6
match_houses(4) ➞ 21
match_houses(87) ➞ 4360 matchsticks.