To solve the above question, we'll use the formula (n-2) × 180. In this question, we are told that it has 10 sides. This implies that n= 10. Therefore, using the formula goes thus:
65 divided by 7 is approximently 9, and 25 divided by 7 is approximently 3, so 9 plus 3 is 12, so Gracie must wash 12 cars to earn enough money to save 25 and spend 65!