To find the percentage of the pond covered by the invasive water weed after 20 weeks, we will evaluate the function \( A(t) = 3e^{0.15t} \) at \( t = 20 \).
First, we calculate \( A(20) \):
\[ A(20) = 3e^{0.15 \cdot 20} \]
Calculating the exponent:
\[ 0.15 \cdot 20 = 3 \]
Now substituting back in:
\[ A(20) = 3e^3 \]
Next, we compute \( e^3 \):
Using approximate value \( e \approx 2.718 \):
\[ e^3 \approx 2.718^3 \approx 20.0855 \]
Now we calculate:
\[ A(20) \approx 3 \cdot 20.0855 \approx 60.2565 \]
To the nearest whole number, this value is approximately:
\[ 60 \]
Thus, the percentage of the pond covered after 20 weeks is 60 percent.