please help. Thank you

Affiliate A sells 7,000 units to Affiliate B per year. The marginal income tax rate for Affiliate A is 25 percent and the marginal income tax rate for Affiliate B is 40 percent. The transfer price per unit is currently $2,000, but it can be set at any level between $2,000 and $2,400. Derive a formula to determine how much annual after-tax profits can be increased by selecting the optimal transfer price. (Do not round intermediate calculations.)