A lot is 21 ft by 30 ft. To support a fence, an architect wants an upright post at each corner and an upright post every 3 ft in between. How many of these posts are needed?

What we know:

Lot = 21 x 30ft

Perimeter=2l+2w

Want to put 4 corner post and one post every 3 ft

What we need to find:

How many post we need.

Perimeter=2 (21) + 2 (30) = 42+60=102ft

102/3=34

34 posts are needed.