Помогите пожайлуста (1-7/10)x=2.1/4 (1/4+1/5)x=1.4/5 (3.1/8+1.3/4)x=2.1/6 (2.1/12-1.5/6)x=3/4

1) x-7x/10=2.1/4; 10x/10-7x/10=21/40; 3x/10=21/40; 10*3x=21*10; 30x=210; x=7; 2) (5/20-4/20)x=14/50; x/20=14/20; 20x=20*14; 20x=280; x=14; 3) (31/80+13/40)x=21/60; (31/80+26/80)x=21/60; 57x/80=21/60; 57x*60=21*80; 57x*60=1680; 57x=28; x=28/57. 4) (21/120-15/60)x=30/40; (21/120-30/120)x=30/40; -9x/120=30/40; -360x=30*120; -360x=3600; x=-10.