Rating Newest Oldest. Best Answer: variable cost = Total Cost-fixed cost $10.00 - $5.00 = $5.00 As output is 1 unit, average variable cost = $5.00 ($5.00 / 1) So, the formula is: variable cost = $5.00 * output.Source(s):Olga Z · 8 years ago. Thumbs up.est Answer: variable cost = Total Cost-fixed cost $10.00 - $5.00 = $5.00 As output is 1 unit, average variable cost = $5.00 ($5.00 / 1) So, the formula is: variable cost = $5.00 * output. Source(s): Olga Z · 8 years ago. Thumbs up.