10000-30*90= 897300
10000-90*90= 891900
10000-1000*90= 810000
400000-720=399280
399280*50=19964000
19964000:100=199640
3.4/5.1=1.4/x
3.4=3 4/10=3 2/5=17/5
5.1=5 1/10=51/10
1.4=1 4/10=1 2/5=7/5
7/5x=17/5:51/10
7.5x=17/5×10/51
7/5x=2/3
x=2/3:7/5
x=2/3×5/7
x=10/21
А. 20-4у-30= 4у+10
б. -72 -8х +50= 8х+22
в. 12а+24-10= 12а+14
г. -38+19х+20= 19х-18
д. 112 - 16а - 90= 16а-22
е. -15х - 60 +60=-15х