Andy is making 3 trapezoidal garden boxes for his backyard. each trapezoid will be the size of the trapezoid below. he will place stone blocks around the borders of the boxes. how many feet of stones will andy need.

The trapezoid in question is an isosceles trapezoid with base lengths of 12 ft and 8 ft and both sides equal to 7 ft.

        8 ft___
       /                    \
7 ft /                      \ 7 ft
     /\
              12 ft

The perimeter of a single trapezoid is:

P = 8 ft + 7 ft + 7 ft + 12 ft = 34 ft

Andy will need 34 ft of stones per trapezoid. So in total:

3 x 34 ft = 102 ft

Andy will need 102 ft of stones in total.