I assumed the bottom of the cylinder is closed. Since Volume is already given, express h in terms of r so that it can be substituted into the Area (A) equation. The question is asking for least surface area, so the differential equation we need to find will be dA / dr. After eqauting dA/dr =0,we can find r and check if the value of r gives us the minimum surface area. From there, you can multiply the Area with the cost to find the minimum surface area cost.

(my r looks like a v so I apologise for that!)