BMAT 2017 Q19 math

Do you explain this question? Is my solution correct?

hey , which is the correct answer ,600?

E is correct answer!

Hi! So it travels the 8 metres to hit the wall and then back to the point and another further 2 metres to hit the other wall then reflect another 2 metres back to the original point. therefore it is a total of 12 m.
12 / 0.001 s = 1200 ms-1