x+6 is x+6. It's an expression. Not sure what you need help with.
If i’m not wrong the answer should be B
Answer: Approximately 72.69 meters
Step-by-step explanation:

Answer : Option D is correct i.e [2.5,4]
Explanation :
Suppose our function is f(x)
then the value of f(x) is minimum where
it reaches -0.44 and 3 with two different intervals .
As we know that for finding the local minimum ,
the criteria is that f'(x)=0 .
So, here
f'(-0.44)=0 and
f'(3)=0
both are the local minimum point for the function f(x)
but -0.44 is the global minimum point .
In our case for [2.5,4] is the required interval where f(x) reaches its local minimum.
2/5 ≥ x - (4/5). add 4/5 to each side
6/5 ≥ x