According to the question,
Consider conical heap,
Base Diameter = 9 cm
So, base radius, r = 4.5 cm
Height, h = 3.5 cm
We know that,
Slant height,
The equation of volume of cone = 1/3πr2h
We know that,
Volume of rice = Volume of conical heap
Volume of rice = 1/3π(4.5)2(3.5)
We also know that,
Canvas requires to just cover heap = Curved surface area of conical heap
And curved surface area of a cone = πrl
Therefore, the canvas required = π(4.5)(5.7) = 80.61 cm2 [appx]