Let the CP of the watch for Vinod be ₹x.
SP = Gain + CP
Now,
SP of the water for Vinod will be the CP of the watch for Arun.
SP of the watch for Arun
= CP − Loss
SP of the watch for Arun will be the CP of the watch for Manoj.
But, CP of the watch for Manoj = ₹3,990
So,
Thus, Vinod paid ₹3,750 for the watch.