Glynn is considering buying a truck and becoming a professinal driver. The truck manufacturer indicates that he can expect his running costs when driving at (v) kilometers per hour to be approx. c(v)=0.85+0.0004(v)^(3/2) where the cost, (c), is in dollars per kilometer. Glynn plans to pay himself 15$/h while he is driving. Find the speed that will minimize his costs for a 1500km trip

I have Ctotal(v)= (0.0004(v)^3/2 + 0.85 + 22500/(v) THIS IS giving me a wack answer need help to solve this derivative

Question

Glynn is considering buying a truck and becoming a professinal driver. The truck manufacturer indicates that he can expect his running costs when driving at (v) kilometers per hour to be approx. c(v)=0.85+0.0004(v)^(3/2) where the cost, (c), is in dollars per kilometer. Glynn plans to pay himself 15$/h while he is driving. Find the speed that will minimize his costs for a 1500km trip 

I have Ctotal(v)= (0.0004(v)^3/2 + 0.85 + 22500/(v) THIS IS giving me a wack answer need help to solve this derivative