I think this is right, it’s been a while since I’ve done this though.
Answer:

Step-by-step explanation:
Data: Area of the room = 750 square feet
Width = Lenght - 5 feet
We have a rectangular room. To calculate it's area we do:
Area = Width x Length
We know that width depends on Lenght in this exercise. Replacing our data above:
750 square feet = (Length - 5 feet) x Lenght
Let's rearrange our equation. If we named Lenght = y :

Now we do one more final step to match one of the options:

If you look carefully, there are two more correct answers similar to the equation above:

Answer:
B. y=[x]+4
when you plug it into the calculator you get b