HS calculus - Not sure about this optimization problem

Question 7: https://imgur.com/fZ8Aapc

l = 2h

lwh = 20,000

w = 10,000/h^2

Cost = 40lw + 2(100hw) + 100lh + 200lw

C'(h) = 6,800,000h^-2 + 600^h^2

I got a ridiculously low value for h, so I must be doing something wrong. What am i missing?