69-12=(60+9)-(10+2)=(60-10)+(9-2)=50+7=57 ;
84-51=(80+4)-(50+1)=(80-50)+(4-2)=30+2=32;
65-12=(60+5)-(10+2)=(60-10)+(5-2)=50+3=53;
82-51=(80+2)-(50+1)=(80-50)+(2-1)=30+1=31;
75-63=(70+5)-(60+3)=(70-60)+(5-3)=10+2=12;
46-35=(40+6)-(30+5)=(40-30)+(6-5)=10+1=11;