The area of the top of the dining table is in the shape of a circle, so the cloth Mary puts on her dining table will have to cover the circular area of the dining table.
The formula to calculate the area of the circle is:
area = pi x radius squared
Where pi could equal 22/7 or 3.14
The diameter is 2 times the radius, so the radius would be diameter / 2
= 6/2 = 3 feet
The area of the circle can be calculated
= pi x 3 squared
= pi x 9
= 28.27 sq. feet
The area of the cloth = area of the circle surface
So material required = 28.27 sq. feet