We start by standardizing the variable. We want to find \(P(X < 3\mu)\).

Standardizing, we have:

\(P(X < 3\mu) = P\left( z < \frac{3\mu - \mu}{4\mu/3} \right)\)

\(= P\left( z < \frac{9\sigma/4 - 3\sigma/4}{\sigma} \right)\)

\(= P\left( z < \frac{6}{4} \right)\)

Using the standard normal distribution table, \(P(z < 1.5) = 0.933\).