Final answer:
Jenny can charge approximately $8 per card to reach her profit goal of $125 in her first month, assuming she sells -15x + 120 cards when charging x dollars per card and retains 70% of the card price as profit.
Step-by-step explanation:
We need to find the highest price x that Jenny can charge for her digital greeting cards to earn $125 in profit in her first month. The profit formula given is -15x + 120 for the number of cards sold, and Jenny earns 70% of the price per card, or 0.7x dollars in profit per card.
First, let's find the total profit equation by multiplying the number of cards sold by Jenny's earnings per card, which is (-15x + 120) × 0.7x. We then set this equation equal to the desired profit of $125:
(-15x + 120) × 0.7x = 125
Now, we expand and simplify the equation to solve for x:
-10.5x² + 84x = 125
Moving 125 to the left side and simplifying, we get:
-10.5x² + 84x - 125 = 0
To solve the quadratic equation, we can use the quadratic formula:
x = [-84 ± √((84²) - 4(-10.5)(-125))]/(2(-10.5))
Calculating the discriminant and then the roots, we find the maximum price Jenny can charge per card. Since the price must be non-negative, we take the positive root of the equation. After calculating, we find that the highest price rounded to the nearest dollar is approximately $8 per card for Jenny to reach her profit goal.