rationalizing the denominator

Note that

sqrt (245)  =  sqrt  ( 49 * 5)  =  7sqrt (5)     and

3sqrt (125)  = 3 sqrt  ( 25 * 5 )   =  15 sqrt (5)  

So....the denominator  is  just      7sqrt (5)  +  15sqrt (5) + 4sqrt (5)  = 26sqrt (5)

So  we have

  6                             3             sqrt (5)                 3sqrt (5)

_________   =   _________  _______     =    ____________

26sqrt (5)              13sqrt (5)   sqrt (5)                    65

$\sqrt{245} = 7\sqrt{5}$

$3\sqrt{125} = 15\sqrt{5}$

This means the denominator can be simplified to:

$(7 + 15 + 4)\sqrt{5} = 26\sqrt{5}$

Which means the entire fraction is:
$\frac{6}{26\sqrt{5}} = \frac{3}{13\sqrt{5}} = \frac{3\sqrt{5}}{65}$