Collinear points A, B and C is shown in the diagram in the picture. The first step in any solution is to draw an illustration so you won't be confused of what are the given information and what is asked of the problem. From the diagram, we know that the length from point A to point C is 3x + 3. According to Segment Addition Property, when a point is plotted in a continuous line, it divides the line into two line segments. When these line segments are added, the value obtained is the length of the whole line. So, in application, line segments AB and BC is equal to the length of line AC.
AB + BC = AC
(-1 + 2x) + 11 = 3x + 3
Simplifying the equation and solving for x,
3x - 2x = -1 + 11 - 3
x = 7