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A fence is to be constructed around a rectangular field. The boards are 12 feet long and fence is 4 boards in height.

Dimensions of field-  660 feet wide and contains 20 acres.

Calculate number of boards needed.  

Let B = number of boards.

Each section contains 48 feet of boards.

20 acres = 871,200 square feet.

How do I proceed from here?  Thanks.

Each panel of the fence is 12 feet long.

Determine the dimensions of the field.
area = 871,200 ft²
Since the width of the field is 660 ft, its length is 871,200/660 = 1,320 ft.
Note that both dimensions (660 ft and 1,320 ft) are divisible by 12, so each side of the fence uses a whole number of panels. Convenient.

perimeter = 2(660) + 2(1,320) = 3,960 ft
3,960 ft × 1 panel/(12 ft) = 330 panels

Each panel is 4 boards high.
330 panels × 4 boards/panel = 1,320 boards

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