What are the dimensions of the pond? .

Let's assume

length of box is l

width of box is w

we know that

area of rectangle = length*width

...................(1)

now, we are given

fencing length is 20 foot

fencing length will be equal to perimeter

and we know that

so, we get

now, we can solve for l

now, we can plug that in first equation

now, we can solve for w

now, we can find length

or

so, option-B..................Answer