A student's work is shown below.
Step 1: 3x 5 = √4x + 6
Step 2: 3x5-6 = √4x6-6
Step 3: 3x11 = √4x
Step 4: (3x - 11)² = (√4x)²

What is the next step in the solution to this equation?

9x² + 121=4x
9x²+121=4x²
9x²-66x + 121 = 4x
9x²-66x121=4x²