Answer:
width = 35
length = 70
Step-by-step explanation:
length (L) = 2w
Perimeter is 2L + 2w
Substitute each variable and solve:
2(2w) + 2w = 210
4w + 2w = 210
6w = 210
w = 35
length is twice that, so 2(35) = 70
