Final answer:
The weight of an individual cannot be calculated directly from the amount of protein they consume (81g of protein). In the context of the given examples, body weight is measured in pounds or kilograms, separate from dietary intake.
Step-by-step explanation:
The question regarding the calculation of an individual's weight based on their use of 81g of protein seems to be a bit vague without additional context. However, looking at the provided Check Your Learning section about the molar mass of a protein and the example about calculating the mass of fat in a person's body, we can answer a related question. The protein intake is not directly used to calculate a person's weight. In the context of the examples given, the weight of an individual is generally measured in pounds or kilograms, and daily protein intake is a dietary consideration. If we look at the example of a 197-lb weight lifter, we can compare against the weight classes in competitions or nutritional requirements for protein intake but not for determining the individual's body weight based on protein usage alone.