Maintain profit margin with new product line

Let m denote million. In Year 2, you introduce a Vegan option with fixed costs of $60m per year for training and $2.25m per month for the supplier. Keep the earlier prices and unit costs (Regular: $4 price, $1 cost; Vegan: $4 price, $2 cost), and keep the Vegan:Regular mix at 2:3. How many total burgers must you sell in Year 2 to maintain the same profit margin as in Year 1 (from the previous question)? Give the general formula and the numeric answer.

Overview: This question tests skill in cost-volume-profit analysis, algebraic modeling of profit margins, and unit economics when a new product line is introduced.