Răspuns :
90-x=80-30
90-x=50
x=90-50
x=40
x-40=50-30
x-40=20
x=20+40
x=60
80-20=70-x
60=70-x
x=80-70
x=10
90-70=x-30
20=x-30
x=30+20
x=50
x- este inimioara
90-x=50
x=90-50
x=40
x-40=50-30
x-40=20
x=20+40
x=60
80-20=70-x
60=70-x
x=80-70
x=10
90-70=x-30
20=x-30
x=30+20
x=50
x- este inimioara