Alright, here is another problem I'm having trouble with. I used a technique I got off of someone on my other thread, and am just looking to see what should be done next. Alright so first I got my equation for the surface area of a cylinder: SA = 2(pi)rh + 2(pi)r^2 and converted 500mL to 0.0005m^3 Then I put in my cost numbers: SA = 1.2[2(pi)r^2] + 0.4[2(pi)rh] Now at this stage I used what I learned in the other thread and got the 'h' out of there by switching the volume formula around (V = (pi)r^2h) and substituting it for 'h'. SA = (1.2)2(pi)r^2 + (0.4)2(pi)r[.0005/(pi)r^2) Now I think I have to simplify and then take the derivative, but when I do that I get dr/dx's and then I get confused and don't know where to go. Anyone give me some tips?