Okay. so we need to show r=2(p+t)

Refer to the figure rohan.

TOX is congruent to RXQ

So that OX = XR

or OR=2*OX -(1)

now, as SP||OT, PX||OT and also TX||OP

so that OPXT is a parallelogram

Now invoking Parallel Law of vector addition, we can say

OP+OT= OX

but from (1)

OP+OT=OR/2

OR=2(OP+OT)

r=2(p+t)

QED

Hope it helps.