I don't understand how this was manipulated

[Saippo]

I'm reading an explanation that involves the atom hitting the wall twice so the distance the atom traveled is 2d along the x direction in time delta t. Then the paragraph concludes that delta t = 2d/vx
So I assumed that it was because vx = 2d/delta t. Is that it? Or is there something that I'm missing? Thanks!

 

[avikarto]

time=distance/speed
t=2d/vx

That's all there is to it.