lets width od field is x , x>0 (if x<0 it is no sense) yards and length is (x+40)yards
So square of field is x(x+40)=6000
x²+40x=6000
x²+40x-6000=0
(x+100)(x-60)=0
x₁=-100 no sense
x₂=60 yards - width of field
x+40=x+60=100 yards - length of field
Answer: 60 yards - width of field, 100 yards - length of field