RS Bisects QT means, it cuts QT in two equal halves, so QP would be equal to PT, as it is an isosceles triangle, one other side would be equal as well, so RP is equal to PS, Now, by ASA, we conclude the both mentioned triangles in the figure are congruent.
It depends if 24cm is the long dimension or the short one...it's the answer if 24cm is the short dim. if 24cm is the long dimension then the answer is 24/1.618
