Length of the sheep pen =60ft
150 ft of fencing bought
One side of rectangular sheep pen is covered with barn which is equaling the width
perimeter of rectangular sheep pen = 2(length +width)
length need to covered is 2 Length+ width
150 =2 length+width
150 = 2 x60 +width
150-120= width
30= width
Area of rectangle = 60 x 30
180 ft2