Financial Calculator Company proposes to invest $12 million in a new calculator making plant. Fixed costs are $3 million a year. A financial calculator costs $10 per unit to manufacture and can be sold for $30 per unit. If the plant lasts for 4 years and the cost of capital is 20%, what is the break-even level (i.e. NPV = 0) of annual rates? (Approximately)(Assume no taxes.)

I need the formula step by step. Like (contribution per unit= selling price - variable cost)