You need to determine the values of a and b for the price demand equation.
The use these values in the marginal revenue equation on the formula sheet. The maximum profit occurs when the marginal revenue is equal to the marginal cost.
This is all covered in detail in my free lectures on pricing (and I obviously can’t type them all out here 🙂 )
(The lectures are a complete free course for Paper F5 and cover everything needed to be able to pass the exam well).