Answer:
69 %
Explanation:
Mark up is Gross Profit expressed as a percentage of Total Costs.
When using variable costing, only the variable costs are used to determine the Product Cost.
Product Cost = Variable product cost per unit + Variable administrative cost per unit
           = $17.00 + $12.00
           = $29.00
Therefore,
Mark up = Profit ÷ Total Variable Cost
       = $20.00 ÷ $29.00
       = 0.69 or 69 %