Hey there! :D
We know that HL is the midsegment, (a segment that is at the midpoint of each side) because of the congruence tick marks.
It will be half of the bases height.
The base is said to be 2.5(JK)
JK= 12. Plug that in.
2.5(12)= 30
Now, we just need to find half of that for the midsegement.
30/2= 15
HL= 15
I hope this helps!
~kaikers