To find \((fg)(x)\), we need to calculate the product of the functions \(f(x)\) and \(g(x)\):
- \(f(x) = 3 \cdot 4^x\)
- \(g(x) = 13 \cdot 4^x\)
Now, let's compute \((fg)(x)\):
\[ (fg)(x) = f(x) \cdot g(x) = (3 \cdot 4^x) \cdot (13 \cdot 4^x) \]
We can combine the constants and the exponential terms:
\[ (fg)(x) = 3 \cdot 13 \cdot (4^x \cdot 4^x) = 39 \cdot (4^x)^2 = 39 \cdot 4^{2x} \]
So, \((fg)(x) = 39 \cdot 4^{2x}\).
Next, we will determine the domain of \((fg)(x)\). Since both \(f(x)\) and \(g(x)\) are defined for all real numbers (as exponentials are defined for all \(x\)), the domain of \((fg)(x)\) is also:
\[ \text{Domain} = (-\infty, \infty) \]
So, the answer is:
\((fg)(x) = 39 \cdot 4^{2x}\) and the domain of \((fg)(x)\) is \((-∞, ∞)\).
None of the provided responses match this. If a more specific answer format is required, please clarify!