They are basically like groups. Take -3x+2x , Just do -3 +2 = -1 and then just add the x. So -1x. Next you have -5y+10y . Just do -5 + 10 = 5 and remember to add the x on so your final answer should be -1x + 5y
This would have to apply for a certain height compared to a weight or vice versa. I'm 5'8'' and for me that would mean I would have a healthy weight of 140 lbs.