<span>20-4х=8(3х+2,5)-2,8х</span>
<span><span>20-4х=24х+20-2,8х</span></span>
<span><span>-4х-24х+2,8х=20-20</span></span>
<span><span>-25,2х=0</span></span>
х=0
<span>4х+9=5(2х-7)-6х</span>
<span><span>4х+9=10х-35-6х</span></span>
<span><span>4х+6х-10х=-35-9</span></span>
<span><span>0=26</span></span>