5х+2*(6-х)=1-3(2x-3)
5x+12-2x=1-6x+9
5x-2x+6x=1+9-12
9x=-2
x=-2:9
x=дробь две девятые
<span>0,2x-0.4=0,5x-2.5
2.5 -0.4 = 0.5x-0.2x
2.1 = 0.3x
x =2.1/0.3 = 21/3 =7
x=7
</span><span>
</span>
А^3-в^3=(а-в)(а^2+ав+в^2)
2*(19+х)+6*19=158
38+2х+114=158
2х=158-38-114
2х=6
х=3 км/ч