Hello, thank you for taking the time to post your question!
The key on this type of question is to find a way to relate the quantities of the given rectangle to one another. On this one we have
Area = L x W = 16
L = 4W
I would plug the second equation into the first to get
(4W)(W) = 16
4W^2 = 16
W^2 = 4
W = -2 or W = 2, but only W = 2 makes sense in this context since we need a positive value for a dimension
So Width = 2, then Length = 4(2) = 8
Meaning that the dimensions here are 2 feet wide by 8 feet long
I hope that helps you get moving in a better direction on this type of question! Feel free to reach out if you have any additional questions beyond that :)