M is the midpoint of AB.
AM = = 4x - 8
MB =
5x-3/3
Find x and AB

X=-7 AB=-72

steps

since m is a midpoint, AM and MB are congruent so you set the two equations equal to each other, 4x-9=5x-3/3( is this a typo? bc 3/3 is 1)
subtract 4x from both sides m, -8=x-1
add 1 to both sides
x=-7

then plug -7 in for x 4(-7)-8=-36
since the two segments are congruent u do -36 x 2= -72