Final answer:
To cover all costs including labor, the number of trees that must be sold is 2.
Step-by-step explanation:
To calculate the number of trees that must be sold to cover all costs, we need to consider the cost of making the party trays and the cost of labor. Since the cost of making the party trays is $14 and the labor cost for an eight hour shift is 7 dollars per hour, the total cost of labor would be 7 * 8 = $56.
To cover all costs, including labor, we need to add the cost of labor to the cost of making the party trays. So, the total cost to cover would be $14 + $56 = $70.
To find the number of trees that must be sold to cover all costs, we need to divide the total cost by the selling price. So, the number of trees that must be sold would be $70 / $35 = 2 trees.