Amir has three parcels.
parcels a and b weigh the same as parcel.
the three parcels weigh 800 grams altogether.
parcel a weighs 250g.
how much does parcel b weigh

So I didn't really understand your question well but, I will try to answer it the best I can. So I'm guessing that parcels A and C weigh the same right? If so, then you would first multiply 250 x 2 ( since you already know that parcel A weighs 250 grams ) then, you would subtract the answer ( which is 500 ) from 800. Now you have your answer which is 300g. I hope this helps I tried my best to answer maybe I got the parcel letters mixed up idk hopefully it helped - Ashlynn