Party trays, which cost $14.00 to make not including labor, are sold for $35.00. If two people work 8-hour shifts making the trays at $7.00 per hour, how many trays must be sold to cover all costs including labor?

Profit on each tray sold excluding labor cost
= $35-$14
= $21
Total labor cost for making party tray for a day
Total labor hours * wages per hour* No. of labors
= $7 * $8*2
= $112
Number of trays must be sold to cover cost will be:
= Total labor cost for making party tray for a day/ Profit on each tray sold excluding labor cost
= $112/$21
= 5.33
5.33 trays must be sold to cover all costs including labor.