Answer:
21 Feet Long
Explanation:
You just reverse how you find a percentage.
1) 40 / 100 = .40
2) .40 * 15 = 6
3) 6 + 15 = 21
I did it this way because I need to find what 40% is to 15. But the trailer isn't 40% of the truck, it's 40% longer than the truck. So, we must add those 2 numbers together getting 21 Ft.