To isolate x, you must first do the reciprocal on both sides, so you do 7/x times x/7 cancel that out, then do it on the other side, so -9/1 x 7/x = -63.
Add all pounds lost during 3 months. 3+7+4= 14. 4 lbsx4 months =16. 16-14=2. 2 lbs must be lost during the 4 month to stay consistent with the 4 lbs weight loss per month.