14: Mr. Schwartz has been hired to paint a row of 7 houses. Each house must be painted red, blue, or green. However, to make it aesthetically pleasing, he doesn’t want any three consecutive houses to be the same color. Find the number of ways he can fulfill his task.
(7 x 3 = 21) is this right?
+680 maybe this will help but it only involves when no 2 adjacent houses can be the same color:
https://ncona.com/2017/02/house-painting-problem/
