Ответ:\((x+2.3)-(x+7.8)=x+2.3-x-7.8=-5.5\).\(-(7.2-y)+(-y+1.6)=-7.2+y-y+1.6=-5.6\).\(-(5.1-2.3x)-(1.1x-0.2)\cdot5=-5.1+2.3x-5.5x+1=-4.5-3.2x\).