Answer:
C. Being at least 20% over one's ideal body weight.
Step-by-step explanation:
Although it's an approximate measure, because the body weight (also known as Body Mass Index - BMI) doesn't accurately measure the obesity, the ratio of body fat in your body is much more representative.
So, yes, generally, being about 20% (some say 25%) over your ideal body weight (BMI) means you can be considered being fat.
Answer A is incorrect, and so is the formula expressed in it.
Answer B is also incorrect, since you can easily weight 200 lbs and still have an ideal weight if you're tall enough.
Answer D cannot be, since A and B are incorrect.