Rideau Co. sells a small plastic toy with a variable production cost of $4 per unit and variable selling costs of $2 per unit. Company annual fixed production and administrative costs total $15,000 and $12,000 respectively. If the selling price per unit was $18 and the company tax rate was 30%, how many units must Rideau Co. sell to earn an after-tax profit of $21,000. (assume all units produced are sold)