Помагите пожалуйста решать уранения

1) 2.5*(4.3-2.1)+10х=17.3
2.5*2.2+10x=17.3
5.5+10x=17.3
10x=-5.5+17.3
10x=11.8
x=11.8/10
x=1.18

2) 100x-8.7*(21.3+8.7)=0
100x-8.7*30=0
100x-261=0
100x=261
x=261/100
x=2.61

3) (15.1+284.9)*0.1-1000x=10.3
300*0.1-1000x=10.3
30-1000x=10.3
-1000x=-30+10.3
1000x=19.7
x=19.7/1000
x=0.0197

4) (237.9+42.1)*0.25-100x=11.2
280*0.25-100x=11.2
70-100x=11.2
-100x=-70+11.2
-100x=-58.8
100x=58.8
x=58.8/100
x=0.588