Final answer:
To calculate the retailer's profit or loss for each unit of Christmas trees, subtract the buying price from the selling price. If the result is positive, it represents a profit, and if it is negative, it represents a loss.
Step-by-step explanation:
The retailer's profit or loss for each unit can be calculated by comparing the buying price and selling price of the Christmas trees. To determine profit, subtract the buying price from the selling price. If the result is positive, it represents a profit, and if it is negative, it represents a loss.
For example, if the retailer buys a Christmas tree for $50 and sells it for $75, the profit per unit would be $75 - $50 = $25. However, if the retailer buys a tree for $75 and sells it for $50, the loss per unit would be $50 - $75 = -$25.