There's one unforgivable taboo that transcends just about every branch of mathematics, and that's dividing by zero. Division by zero is undefined, so any fraction with a zero in its denominator is by definition absurd. For what values of x would the denominators on either of those fractions be zero? Those will define the restrictions on your variable.
(24, 12) and (36, 0). The least amount of flowering plants occurs when x=2y, and the largest amount occurs when y=0. These two points satisfy both conditions and both sum to 36.
