Final answer:
The patient weighs 128.5 lbs.
Step-by-step explanation:
To determine the patient's weight using a balance scale, you subtract the lower calibration bar's reading from the upper calibration bar's reading. In this case: 150 (upper bar) - 21.5 (lower bar) = 128.5 lbs. So, the patient's weight is 128.5 lbs. Therefore, the correct answer is: b) 128.5 lbs It's essential to understand how to interpret the readings on a balance scale to accurately assess a patient's weight. This type of scale relies on the principle of balancing weights, and the difference between the upper and lower readings indicates the patient's weight in pounds or kilograms, depending on the scale's calibration.