each hit on a pin is 1/2 probability.

the ball has 3 paths:
left, left, right = (1/2)x(1/2)x(1/2)
left, right, left = (1/2)x(1/2)x(1/2)
right, left, left = (1/2)x(1/2)x(1/2)

add them all up = 3/8

Kelly wrote:This question is what I wrong from Prep.

How can I solve this?

The easiest way is to use the mouse and visualize the different tree branches that lead to 2. If you can't visualize then redraw the diagram on paper and draw the branches.After the first level, if you move each level below you multiply by 1/2. Draw Left rigt branches. Example. Begining from level 1 and branching left and right first series that that ends in 2 is:

LLR

The 2nd is:
LRL

3rd is:
RLL

Each one of these is 1/8. Adding all 3 gives the OA 3/8.

This is one of those problems that looks harder in appearance but is actually very very easy.
Hope this helps.