A form of radium decays exponentially with a half-life of 20 years. This means that 50% will be gone every 20 years. A human can only withstand an exposure of 5 grams of this radium but 150 grams has leaked into the air. Part A: Write an equation to model the exponential decay of this 150 grams of this form of radium.

Part B: A scientist claims that the area will e safe for humans after 100 years. Do you agree? Verify your answer mathematically and explain why you agree.