Answer:
[tex]Area = (30 + x)(20 + x)[/tex]
Step-by-step explanation:
By definition, the area of a rectangle is the product of its length multiplied by its width.
Initially the dog run has a length of 30 ft long and 20 ft wide.
If you want to expand the track, increase the length of each side by a factor x. So, the dimensions of the expanded dog run will be:
[tex]Length = 30 + x\\Width = 20 + x[/tex]
Then, the area is:
[tex]Area = Length * Width[/tex]
[tex]Area = (30 + x)(20 + x)[/tex]