Drawing Moving Bar

I got this code I made:

Now, the bar that is drawn is extending to the right, I’ve positioned the bar at the end point but have no clue on how to back it extend to the left. Any ideas?

bad reader

Not sure you understand, all I need to know is how to make the bar extend backwards.

	draw.RoundedBox(0, 100, ScrH() - 72, 250, 50, healthColour)
	draw.RoundedBox(0, 100, ScrH() - 72, 250 - speedWidth, 50, Color(100,100,100))

I tried this and it works, but is there any other clean way of doing this?