Răspuns :
a+200=800 b-500=200
a=800-200 b=200+500
a=600 b=700
c+300=900 900-d=400
c=900-300 d=900-400
c=600 d=500
a=800-200 b=200+500
a=600 b=700
c+300=900 900-d=400
c=900-300 d=900-400
c=600 d=500