I’m kind of embarrassed that I’m not getting the same solution because I understand the whole thing and theory but still I get 24 and in the video the answer given is 56.What am I overlooking

Isn’t it so that
320 = (40 - x ) . 20
320 / 20 = 40 - x
16 = 40 - x
-24 = -x and so x = 24?

Ah ok so, yes this makes sense. So then what’s in the video stating
320 = (40-x) . 20 is not the proper way of setting up the equation because that will never turn into 56, right?