a) In terms of the areas of the circles:
.. walkway area = π*(11 m)^2 -π*(9 m)^2 = π*(121 -81) m^2 = 40π m^2
In terms of the length of the walk and its width:
.. walkway area = 2*π*(10 m)*(2 m) = 40π m^2
b) The approximate area is
.. 40*3.14 m^2 = 125.6 m^2
