Taxable Value in GST Return

There are 2 condition :

1. Mr Y can charge Rs 15 as job work from Mr X & Mr X has to send the Garlic on Delivery Challan (In term of rule 45) . In this case Mr. Y can report Rs 15/- As a outward supply in his GSTR 1.

2. As per you when Mr. Y has raise the Bill for 75/- then his outward supply is 75/- & the same is to report in GSTR 1

Note : it's recommended ,You should adopt Option 1