The manager of a local monopoly

I need help with the following question:

The manager of a local monopoly estimates that the elasticity of demand for its product is constant and equal to -3. The firm’s marginal cost is constant at $25 per unit.

a. Express the firm’s marginal revenue as a function of its price.

Instruction: Round your response to 2 ;decimal places.

MR = ____ x P

b. Determine the profit-maximizing price.

Instruction: Use the rounded value calculated above and round your response to 2 decimal places.

$ ___________