We recognize that the expression \( \left( 1 + \frac{4}{x} \right)^x \) is a form of the limit definition of the exponential function \( e \). As \( x \to \infty \), we have:
\[
\lim_{x \to \infty} \left( 1 + \frac{4}{x} \right)^x = e^(4)
\]
Thus, the limit becomes:
\[
\lim_{x \to \infty} 5 \left( 1 + \frac{4}{x} \right)^x = 5e^(4)
\]