Answer
Length is $200~\text{m}$ and width is $110~\text{m}$
Work Step by Step
Let the length be $L$ and width be $W$.
Two times width is $20$ m bigger than length:
$$L=2W-20$$
Perimeter is $620$ m:
$$2L+2W=620$$
Substitute $L=2W-20$:
$$2(2W-20)+2W=620$$
$$4W-40+2W=620$$
$$6W=620+40$$
$$6W=660$$
$$W=660:6=110$$
Find length:
$$L=2\cdot 110-20=200$$
