because ΔCDF is similar to ΔBDE, the corresponding sides are proportional
CD:BD=FD:ED
(3.63+5.19):5.19=(x+4.45):4.45
5.19(x+4.45)=(3.63+5.19)*4.45
5.19x+5.19*4.45=3.63*4.45+5.19*4.45
5.19x=3.63*4.45=16.1535
x≈3.11
you can also do DB:BC=DE:EF. You'll get the same result.
