plug in the answers to see which has an equal scale factor between mp and mt, and po and tr
if tr = 6, then the scale factor between po and tr is 1.5
that means, that in order to equal 9 mt would have to be 3
if mt = 3, then the scale factor between mp and mt would also be 1.5
therefore, since they both have an equal scale factor, the answer is
4) TR = 6
hope this helps!!