[tex]\text{r = }\dfrac{\sqrt{G*m_1*m_2}}{\sqrt{F}}[/tex]
This is what is in the middle of the second paragraph. That statement is correct.
I don't know that it is any simpler or not, but what they have done in the answer is rationalize the denominator. That means that the denominator is no longer under the square root sign.
To get that result, you multiply numerator and denominator by √F
When you do that, your get
[tex]\text{r =}\dfrac{G\sqrt{m_1*m_2}\sqrt{F}} { \sqrt{F*}\sqrt{ F}}[/tex]
This results in the middle answer.
[tex]\text{r = } \dfrac{ \sqrt{G m_1*m_2*F}}{F}[/tex]