Kindly verify the workings eh, thanks.

Find area

Find volume

Area is base + side

Material is area x thickness

Side is found by cutting the cylinder and becomes a rectangle with width as 2PI()R

Form equation don’t put in number

V = base area x height
Mat = thickness x Area
Area is as indicated

Then differentiate mat against R
Then differentiate mat again against R to show it is minimum as always > 0

During the journey you will find that thickness is redundant

Find R expressed in V as constant

Find H expressed in V as constant

Both happen to be the same

Then put V=1000, R and H is the answer