Notice that we're looking at a set of similar triangles, we can say that:
[tex]RS\parallel QP[/tex]
Now, since RS is parallel to the base of the big triangle, and also connects segments QT and PT by their midpoints, we can say that
[tex]QP=2RS[/tex]
Therefore, if QP = 16, then RS = 8 ; and if RS = 9 , then QP = 18
