Explanation: 20-2.4=17.6 feet That is the length of the wall not counting the painting. 17.6/2=8.8 8.8 is the measurement of one side of the painting to the end of the wall.
The length is 12, because if it's 9 inches wide it has two sides of 9 inches which is 18. Then subtract that from the intial value 42 to get 24. After, you divide 24 by 2 due to there being 2 sides of the box and 24 is the sum of both sides. Hopethis helps!
