Calculating Breathing Rate Increase Steps:

• Identify resting breathing rate from provided data (e.g., 12 breaths per minute).
• Identify exercise breathing rate from provided data (e.g., 21 breaths per minute).
• Subtract resting rate from exercise rate: 21 - 12 = 9.
• The result is the increase in breaths per minute.

Why A is correct:

• The increase is the difference between exercise and resting rates, which equals 9 breaths per minute per the calculation.

Why the others are wrong:

• B: 12 matches the resting rate, not the increase.
• C: 21 matches the exercise rate, not the increase.
• D: 60 is an unrealistically high exercise rate, not the calculated increase.

Not enough information: Specific rates are not provided in the question text.

Final answer: A