Kevin timed himself and he found that he can eat more bowls of honey bunches of oats in 60 minutes write an equation to represent this equation. write the equation in y=mx form

Let Width = W, then Length = L = 5000/W

Apply the $4 fence on the shorter side W, then  total cost
C(W)=$4*(2W)+$2*(2L)
=(8W^2+20000)/W
To find the minimum cost, differentiate C(W) with respect to W and equate to zero and solve for W:
C'(W)=(8W^2-20000)/W^2=0 => 8W^2-20000=0 =>
W=sqrt(20000/8)=50'
Length L=5000/50=100'

We now need to check that W indeed gives a minimum cost C(W).
This can be done by checking the sign of C"(W), the second derivative.
The second derivative C"(W)=40000/W^3 >0, which means that W=50 gives a minimum value for C(W).
The total (minimum) cost is therefore
C(50)=(8*50^2+20000)/50=$800
check average cost = $800/(2(50+100))=$800/300=$2.67 / foot, 
which is between $2 and $4, and that sounds reasonable!