what did he do wrong? pls help ill give brainliest

Answer:
Between step 4 and final answer, the incorrect square root is used as a multiplier
Step-by-step explanation:
Process should be
-5√11 + 15√(6 • 4)
-5√11 + 15√6 • √4
-5√11 + 15√6 • 2
-5√11 + 30√6