Perimeter of a rectangle

Hello all. My first post here and I hope you will be able to help me out. I am an undergrad student. I have only a few classes left and will be graduating with honors, providing I don't fully drop the ball in math. I have to take two math classes, college mathematics 1 and 2. Once these classes are done, I am all but finished.

I use several tutoring tools and use the examples and tutorials given, but I am having a hard time associating some questions with the examples I've practiced.

Here is one set of problems I am working on. Any help would be appreciated. Thank you in advance.

Perimeter of a rectangle. A rectangle has a fixed width and a variable length. Let P represent the perimeter and L represent the length. P=28 inches when L=6.5 inches and P=36 inches when L=10.5 inches. There is a linear equation that expresses P in terms of L.
a) Find the equation.
b) What is the perimeter when L=40 inches?
c) What is the length when P=215 inches?
d) What is the width of the rectangle?

If I am understanding correctly, would the formula to answer 'a' be:

Perimeter = 2(side a)+2(side b)

Then I can plug in:
28=2(6.5)+2(x)

and

36=2(10.5)+2(x)

Does this look like I am on the correct track, please?

This is what I have come up with. Please let me know if I am on the right track in understanding this.

Thanks.

90. Perimeter of a rectangle. A rectangle has a fixed width and a variable length. Let P represent the perimeter and L represent the length. P=28 inches when L=6.5 inches and P=36 inches when L=10.5 inches. There is a linear equation that expresses P in terms of L.
a) Find the equation.
Answer: P=2(side a)+2(side b)
b) What is the perimeter when L=40 inches?
Fixed width (W) = 7.5
Answer: P=2(40)+2(7.5). P=95 inches
c) What is the length when P=215 inches?
215=2(x)+2(7.5)
Answer: x=100 or Length is 100 inches
d) What is the width of the rectangle?
Answer: Based on the initial information, the width (W) is 7.5 inches.