25x(4+12)=25x4+25x12=100+25x4x3=100+100x3=100+300=400
=25x4＋25x4x3=100+300=400
25x(4＋12)=25x(4＋4+8)=25x4＋25x4+25x8=100+100+200=400
=25x16=25x4x4=100x4=400
25x(4＋12)=25x4+25x4x3=100+100x3=400
