Answer
AB=21
Solution
In the triangle ABC two lines are parallel to side AC.In a triangle a line passing through two side and it is parallel to third side,then this line divides two side in equal ratio.
Here we take any of the parallel line, passing through AB and AC, and parallel to BC.
So we can write,[tex]\\[/tex][tex]\frac{ 6x+2x+1}{2x}[/tex]=[tex]\frac{18+7.5}{6}[/tex]
8x+1=6x+2.5x
x=1/0.5
x=2
Therefore AB = 6x+2x+1+2x =10x+1=21
