"Comparing linear rates word problems": a Test Quiz question from the Algebra 1 module

I don't get how Khan went from:

15cm -5cm/6hours * t = 25cm - 15cm/6hours * t

to ...

10cm/6h * t = 10cm

It's the 10cm side of the equation that has stumped me for over an hour. For me, there's a step or two missing and I can't work it out. Thx.