A line segment bisector passes through the midpoint of the segment. So the segment bisector of JK is M.
Also, the length of JM is 7x + 5, which we know is equal to 8x, so we just have to find x and then figure out the length.
7x + 5 = 8x subtract 7x from both sides
5 = x
Does it work? Let's see. 7(5) + 5 = 40 AND 8(5) = 40
The length of JM is 40.