2012.25*2013.25-2010.25*2015.25
=(2010.25+2)*(2015.25-2)-2010.25*2015.25
=2010.25*2015.25-2*2010.25+2*2015.25-4-2010.25*2015.25
=2010.25*2015.25-2010.25*2015.25-2*2010.25+2*(2010.25+5)-4
=-2*2010.25+2*2010.25+2*5-4
=2*5-4
=6
2012.25*2013.25-2010.25*2015.25
=(2010.25+2)*(2015.25-2)-2010.25*2015.25
=2010.25*2015.25-2*2010.25+2*2015.25-4-2010.25*2015.25
=2010.25*2015.25-2010.25*2015.25-2*2010.25+2*(2010.25+5)-4
=-2*2010.25+2*2010.25+2*5-4
=2*5-4
=6