Final answer:
Advise the client to increase intensity and frequency of training, focus on diet and exercise, and consider a more gradual progression for muscle gains.
Step-by-step explanation:
To help your client achieve his goal of adding 20 lbs. of muscle in 3 months, you should advise him to increase the intensity and frequency of his training sessions. He should aim to lift heavier weights and perform more challenging exercises during each session. Additionally, he should focus on both diet and exercise for optimal results. Proper nutrition, including adequate protein intake, is essential for muscle growth. However, it's important to note that gaining 20 lbs. of muscle in 3 months may not be achievable. It is generally recommended to aim for a more gradual and sustainable progression for muscle gains.