(3/2-7/4)x2+5/4
=3/2*2-7/4*2+1+1/4
=3-7/2+1+1/4
=3+1-7/2+1/4
=4-7/2+1/4
=1/2+1/4
=3/4对不起啊，题目弄错了。（三分之二减七分之四）乘二加五分之四