Answer:
16
Explanation:
3x + 4 = x + 12 [The straight line on the segments AB and BC indicate that they are the same length]
2x = 8 [Subtract x and 8 from both sides]
x = 4 [Divide both sides by two]
Length AB is equal to (3x + 4) as indicated by the diagram. Substituting x = 4, (3 * 4) + 4 = 16