Răspuns :
a+b+c=28
a+b=21 => c=28-21=7
b+c=17 => b=17-7=10
a+b=21 => a=21-10=11
verificare:
a+b+c=11+10+7=28
a+b=21 => c=28-21=7
b+c=17 => b=17-7=10
a+b=21 => a=21-10=11
verificare:
a+b+c=11+10+7=28