1/x divided by 1/y equals

Astick 2 m long is placed vertically at point b. the top of the stick is in line with the top of a tree as seen from point a, which is 3 m from the stick and 30 m from the tree. how tall is the tree?

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Can you me find the missing length. i attached an image.