Answer:
The length of blue segment is:
9
Explanation:
We know that the:
Length of transverse axis i.e. '2a' is equal to 6.
i.e. 2a=6.
Also the distance of a point from one focus is 15.
and let the length of the blue segment be 'b'.
" As we know that the absolute value of the difference of distance of a point from the two focus is equal to the length of a transverse axis "
Hence,

Hence, we have:

Hence, the length of the blue segment is:
9