how GST works for health agrigator

Hi sir one of my client is an an health agrigator he take lab and other medical services from hospital and clinics across country and give it to customers. can please explain how does GST works.

example he gets an sugar test for his client from Apollo hospital.Hospital charges him Rs.100 and he keeps an margin of Rs.10.How much he needs to charge client.

Apollo hospital is exempted by GST for sugar test.How he needs to bill the client.
Agrigator needs to pay GST for his margin or for Rs.110.

Request to clarify