An empty fuel tank of a car was filled with A type petrol. When the tank was half-empty, it was filled with B type petrol. Again when the tank was half empty, it was filled with A type petrol. When the tank was half-empty again, it was filled with B type petrol. What is the percentage of A type petrol present in the tank?
a. `33. 5 %`
b. `37. 5 %`
c. `40 %`
d. `50 %`