An object is placed in front of a plane mirror of length $L$ ...

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I am stuck on the following problem :

An object is placed in front of a plane mirror of length $L$ at a distance $d$ of its bisector line .An observer is at a perpendicular distance of $2d$ from the mirror.If the observer is walking parallel to the mirror ,upto what maximum possible distance he can observe the image of that object . The options are

(a) $2L\,$ (b) $\,3L\,$ (c)$\,4L\,$(d)$\,5L\,$

Can someone please explain ?

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Here are diagrams of what's going on:

enter image description here

enter image description here

You can work out how long the line at the bottom is by comparing the big triangle with the little triangle. They are similar triangles.