Elissa wants to set up a rectangular dog run in her backyard. she has 30 feet of fencing to work with and wants to use it all. if the dog run is to be x feet long, express the area of the dog run as a function of x.

a. a(x)=14x-x^2
b. a(x)=15x-x^2
c. a(x)=17x^2-x
d. a(x)=16x-x^2