Ballard Company's variable costs are one-third of its sales. Its fixed costs are $5 per unit when 6,000 units are sold. Approximately how many units does the company need to sell to earn $10,000 in net income if the sales price per unit is $18?
The solution to work out is, 18x = 6x + 30,000 + 10,000. I understand where everything comes from except for the "6x". How is this described in the function?