1)(3x + y) - (-x - 4y)=3х+у+х+4у=4х+5у; ///
2)(x + 6y) - (8x - 7y)=х+6у-8х+7у=13у-7х; ///
3)(m + n) - ( m - n)=m+n-m+n=2n; ///
4)( m + 3) - (6m +5) - (m -1)=m+3-6m-5-m+1=-1-6m; ///
5)(x - y) + (x - y) - (2x + y)=x-y+x-y-2x-y=-3y; ///
6)(0,2x - 3) - ( x - 2) - (0,4x - 1)=
0,2х-3-х+2-0,4х+1= -1,2х