Emily subscribes to an online learning platform for $15 per month, which allows her to purchase courses at a discounted rate of $5 per course. The equation (y = 15x + 5, 15y = 5x, y = 15 + 5x, or 15 = 5x + y) represents the total amount Emily spends each month on learning, where x represents the number of courses she buys. If Emily spent $60 in August on courses, then she purchased (10, 6, 4, or 9) courses that month.