To expand the expression \((\sqrt{x} + 3x) \cdot 4 + (\sqrt{x} - 3x) \cdot 4\), we can start by distributing the \(4\) in both terms.
- Distributing \(4\) in the first term:
\[ (\sqrt{x} + 3x) \cdot 4 = 4\sqrt{x} + 12x \]
- Distributing \(4\) in the second term:
\[ (\sqrt{x} - 3x) \cdot 4 = 4\sqrt{x} - 12x \]
Now, we can combine the expanded results:
\[ (4\sqrt{x} + 12x) + (4\sqrt{x} - 12x) \]
Now, combining like terms:
- For \(\sqrt{x}\):
\[ 4\sqrt{x} + 4\sqrt{x} = 8\sqrt{x} \]
- For \(x\):
\[ 12x - 12x = 0 \]
Putting it all together:
\[ 8\sqrt{x} + 0 = 8\sqrt{x} \]
Thus, the final expanded expression is:
\[ \boxed{8\sqrt{x}} \]