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.