（1）2-6/13*26/9-2/3
=2-4/3-2/3
=2-(4/3+2/3)
=2-2
=0
(2)1/4*39+3/4*25+3/4*14
=1/4*39+(3/4*25+3/4*14)
=1/4*39+3/4*(25+14)
=1/4*39+3/4*39
=39*(1/4+3/4)
=39*1
=39