The way I read the table, 40 in the Total cost column (when product quantity is zero) is the fixed costs.
Then each line add employee hours, which you multiply by hourly rate ($10) and add to fixed costs = total costs. They will grow as the employee hours increase.
Marginal cost is the difference between the two lines of total cost (one above and one below).
Your variable costs here is $10/hour of employee time.