Question 846648
The radius of the garden is {{{ 20/2 = 10 }}} ft
The area of the garden is:
{{{ A[1] = pi*r^2 }}}
{{{ A[1] = 3.14*10^2 }}}
{{{ A[1] = 314 }}} ft2
--------------------
The area of the border plus the garden is:
{{{ A[2] = 3.14*( 10+3 )^2 }}}
{{{ A[2] = 3.14*169 }}}
{{{ A[2] = 530.66 }}}
-------------------
The area of the border is:
{{{ A[2] - A[1] = 530.66 - 314 = 216.66 }}} ft2
----------------------------------------
The volume of concrete in the border is:
{{{ V = 216.66*.5 }}} ( 6 in = .5 ft )
{{{ V = 108.33 }}}  ft3
---------------------