Question 858989
Diameter including walkway = 80 feet 
so radius = 40 feet

the width is 5 feet
so the garden radius = 35 feet

Area of walkway = total area - garden area

Total area = pi*r^2
=pi*40^2

garden area = pi*35^2

Difference = pi*40^2-pi^35^2

=pi(40^2-30^2)
= 121 sq.ft


10 sq.ft ----------------1 bag
121 sq.ft ---------------?

121/10

=12.1 bags

= 13 bags  of gravel