B is the midpoint of line AC. AB=x+6 and AC=3x-31. What is the length of line BC

BC = 49

Step-by-step explanation:

Since B is the midpoint,  AB is half of AC & AB equals to BC

3x-31 = 2(x+6)           >> distribute 2 (AB is doubled here since AB=BC)

3x-31 = 2x+12            >> add 31 to both sides

3x = 2x+43                >> subtract 2x from both sides to get x alone

x = 43

AB=BC so you can use AB's equation

BC = x + 6

BC = (43) + 6

BC = 49