(3/4+1/6)×3+(5/6-1/2)÷2/9=((2*3+3*1)/12)3+((6*5-2*1)/12)*9/2=(9/12)*3+(28/12)*9/2=9/4+14*3/4=9/4+42/4=51/4=12,75
б) (1 1/5+2 3/10)÷1/2+(6 3/4-2 2/3)÷1 1/6=(6/5+23/10)*2+(27/4-8/3):7/6=((6*2+23)/10)*2+(27*3-8*4)12)*6/7=(35/10)*2+(49/12)*6/7=35/5+7/2=7+3,5=10,5