The perimeter of a shape is the length of all the sides added together. In this problem, the length of the rectangle is x and the width is (2x-5). With the information given, we want to show that it equals or is equivalent to (6x-10), which is supposed to represent the perimeter of the rectangle.
Before I write my equation I what to make sure you understand that there are of course two side lengths of this rectangle and two widths. That being said, the equation would look like this:
2x + 2(2x-5) = 6x-10
(both side lengths) + (both widths) = perimeter
I'll show you how you can simplify this equation to show that the perimeter of the field is 6x-10 :
2x + 2(2x-5) = 6x-10
(first step would be to distribute the 2 into 2x-5)
2x + 4x-10 = 6x-10
(add the x's on the left side to simplify)
6x-10 = 6x-10
Well well, what do we have here :). We ended up with the same expression on each side of the equal sign. We totally know that they're equivalent, in fact they're the same.
(I honestly really hope this helps. I confused myself a little thinking a lot about this problem. Please let me know if you run into any issues with my answer. I'm pretty sure I'm accurate on the work I showed. I also wasn't able to view your PDF sadly :( )