B is the midpoint of AC. AB X+6; AC = 3x - 31 AB =... BC = .... thats all it says

Answer 1

So then 3x-31 = 2(x+6)

3x - 31 = 2x + 12

x - 31 = 12

x = 43

SO AB=BC = 43+6 = 49 and 2(49) = 98 = 129-31 = 3(43)-31 = 3x-31

Answer 2

If AB = BC, then AB also equal X+6.

Also, AB + BC = AC, by segment addition postulate

Since AB = BC = x + 6 and AC = 3x -31,

x + 6 + x + 6 = 3x - 31

2x + 12 = 3x - 31

43 = x

so AB = BC = x + 6 = 43 + 6 = 49

AC = 3x - 31 = 3(43) - 31 = 98