Lets say the loser had y points

So y+4 is the winners point

Now lets consider that winner won a , drew b & lost c

a+b+c= 15_______________(0)

a + 0.5b= y+4 ___________________(1)

But the loser had y points given by

c+ 0.5b = y_____________________(2)

Add 1 and 2

a+b+c= 2y+4

But this is same as (0)

Hence 2y+4 = 15

2y= 11

y= 5.5

(b)