Dear Akshay,
I believe I understand how this all is coming from.
Firstly, the restaurant has not provided any breakup of the Service and Food element. The Rs.75.7/- merely seems to be the TIP collected separately by most of the restaurants. This tip is later distributed amongst the staff.
Thus, it is merely a reverse calculation mechanism by which we may come to know the calculation, viz.
Service tax @ 4.944% - Rs.39.28/-
Thus, Net Food value - Rs.794/-
Total Rs. - Rs.833/-
In this, way, you can understand that the Restaurant has not shown a separate break-up of net value.
Moreover, it even did not charge VAT on it. Not sure, why.
But, I am pretty sure, this is how it has been calculated.