Question 842353
From the center of the tree to the inner edge of the walk is 3 feet. 
From the center of the tree to the outer edge of the walk is (3+8) 11 feet.
The area of cement is the area of a circle with radius of 11 feet minus the area of a circle with a radius of 3 ft.
The area of a circle is,
{{{A[circle]=pi*r^2}}}
The area of the cement is then,
{{{A[cement]=pi(11^2-3^2)=pi*(121-9)=112*pi}}}