Without way bill

Suppose Mr. X purchased a computer which Gross value 103,500.00 dated 09/06/2018 from Mr. Y within state(West Bengal). But Mr. Y not issue any WAY BILL against this, Computer Delivery to Mr. X  through  Motor Cycle. Mr. X also not create any WAY Bill (Inward) for this above. Note that Both party are register in GST Act. 

Now Question is

1) Penelty is applicable for this

2) Who paid penlty Mr Y or Mr. X or both