Answer:
No, it's doesn't mean you are not smart. Just maybe you need to focus on learning most of the things to solve in math, you need to start with what is given to you.
Here given to you that every scale of 2 in = 8ft in actual truck.
So in order to know what 6in equals. Break down 6 into something you can use which is 2in = 8ft
6 = 2 + 2 + 2
So 6in = 8ft + 8ft + 8ft
Which can be simplified to 6ft = 24 ft.