① 0.74-3/4÷2/3+2/5②5/4÷(3/2-0.25+9)③2÷6/13/9/39+2/3④3/4×2/5+3/5×4/3(要过程,要答案,最好用六年级知识!)(急急急急急急急急急急急!!!!!!)