Error: She did not fully simplify [tex]\sqrt{12x^{3}}[/tex]
Correct simplification:
[tex]5x\sqrt{48x^{5}}\\\\=5x\sqrt{16x^{4}}\sqrt{3x}\\\\=5x(4x^{2})\sqrt{3x}\\\\=20x^{3}\sqrt{3x}[/tex]