1) 23.6+(14.5-30.1)-(6.8+1.9)
23.6+(-15.6)-8.7
23.6-15.6-8.7
-0.7
3) 0.6(x+7)-0.5(x-3)=6.8
0.6x+4.2-0.5x+1.5=6.8
0.1x+5.7=6.8
0.1x=6.8-5.7
0.1x=1.1
x=11
4)0.8x+0.3(x+4.9)=25.56
0.8x+0.3x+1.47=25.56
1.1x=25.56-1.47
1.1x=24.09
x=24.09:1.1
x=21.9
21.9+4.9=26.8-стоимость 1 кг сыра