To evaluate the function \( f(x) = 4.25(6x) \) at \( x = 4 \), substitute \( x \) with 4:
\[ f(4) = 4.25(6 \cdot 4) \]
First, calculate \( 6 \cdot 4 \):
\[ 6 \cdot 4 = 24 \]
Now, substitute this value back into the function:
\[ f(4) = 4.25 \cdot 24 \]
Next, calculate \( 4.25 \cdot 24 \):
\[ 4.25 \cdot 24 = 102 \]
Thus, the value of the function at \( x = 4 \) is
\[ \boxed{102} \]