If You mark 6 at your number line and want to minus 8 think about it like temperature. That now is 6 degrees and it is getting cooler 8 degrees. In our case we don't have thermometer, but number line. So we can't move down (like in thermometer), but we can move to left. Just start moving to the left (because of minus) and count to 8 and stop. You will stop at -2 and its result 6+(-8)=-2
