2) 0,7x-(2y-0,7x)=0,7x-2y+0,7x=0,7x+0,7x-2y=1,4x-2y

4)2/3(m-3n)+1/3(n-2m)=2/3m-2n+1/3n-2/3m=2/3m-2/3m-2n+1/3n= 1  3/3n-1/3n=1   2/3n

6)3(c+d)-7(d+2c)=3c+3d-7d-2c=3c-2c+3d-7d=c+4d