Thanks for the puzzle.
Should be 5.
If 3 boys are 30 then 1 boy = 10
Again 2 boys and 1 bottle of syrup is 40; hence one 1 syrup bottle should be 40 - 20 = 20
Basis above,
1 Boy + 2 bottles of syrup (it seems 2 bottles from the pic) + 2 glasses of milk = 60
which is 10 + 40 + 2 glasses of milk = 60
or, 1 glass of milk = 5