How to calculate gst

Dear sir,

This ramesh, I am accountant in automobile 🚗 delear company in hyderabad ,My Quasion  is one vehicle (luxury car) come to our workshop for car serviceing, we change spare parts and also charge labour charges, so how to calculate gst tax 

Ex: total parts value is 26000

Labour charges 5000

So how to calculate gst tax and total bill amount