Segments either side of an angle bisector are proportional.
The longest the third side (x) could be is
 6/5 = x/6.9
 x = 6/5*6.9 = 8.28
The shortest the third side could be is
 5/6 = x/6.9
 x = 5/6*6.9 = 5.75
The longest and shortest possible lengths for the third side are ...
 8.3 cm and 5.8 cm.