Answer: BC is 4 units
If point B is the midpoint of line AC, then the distance from A to B is equal to the distance from B to C. This can be expressed as: AB = BC
Given that AB equals X + 6 and BC equals 5X - 6, we can set up an equation: X + 6 = 5X - 6
Now, solve for X
6X = 12
X = 2
Now that we have the value of X, we can find BC:
BC = 5X - 6
BC = 5 * 2 - 6
BC = 10 - 6
BC = 4
So, the length of BC is 4 units