①13X-6.8X+X=46.8,
x(13-6.8+1)=46.8,
7.2x=46.8,
7.2x÷7.2=46.8÷7.2,
x=6.5;
②2.7×2-1.5X=0,
5.4-1.5x=0,
5.4-1.5x+1.5x=0+1.5x,
1.5x=5.4,
1.5x÷1.5=5.4÷1.5,
x=3.6;
③0.9÷(x+0.4)=0.45,
0.45×(x+0.4)=0.9,
0.45×(x+0.4)÷0.45=0.9÷0.45,
x+0.4=2,
x+0.4-0.4=2-0.4,
x=1.6.