Find what he did wrong and fix it. Need answer fast with all the steps included please. NEED HELP

Simplify The numerator
[tex]4 {a}^{2} - {b}^{2} = (2a + b)(2a - b)[/tex]
[tex] \sqrt{ \frac{(2a + b)(2a - b)}{9a} } [/tex]
[tex] \sqrt{9a} = \sqrt{9} \times \sqrt{a} [/tex]
[tex]3 \times \sqrt{a} [/tex]
[tex] \sqrt{ \frac{(2a + b)(2a - b)}{3 \sqrt{a} } } [/tex]
RATIONALIZE
[tex] \frac{ \sqrt{a} \sqrt{(2a + b)(2a - b)} }{3 \sqrt{a } \times \sqrt{a} } [/tex]
[tex] \sqrt{ \frac{a(2a + b)(2a - b)}{3a} } [/tex]. This is the answer