The line LH bisects segment GK, this means that it divides segment GK exactly trough its midpoint.
Segments GL is equal to segment LK and both add up to GK:
GK= GL + LK
GL=LK= 5x-5
Using this equality you have to replace the segments names by the given expressions and clear the value of x.
Now you can use the value of x to calculate the length of GK
GK=8x+6=8*8+6=70