a) (257+23)•(413-63)=
=280•350=
=98000
b) (2+4+6+8+10+12)•(1+3+5+7+9)=
=(6+6+8+10+12)•(4+5+7+9)=
=(12+8+10+12)•(9+7+9)=
=(20+10+12)•(16+9)=
=(30+12)•25=
=42•25=
=1050
