А=2,8-1,3=1,5
б)=3,3+2,1=5,3
в)=11,5-7,9=3,6
д)=12,8+13,9=26,7
<span> \left \{ {{2y-4>3y+1} \atop {5y+5<4y+3}} \right. \left \{ {{-y\ \textgreater \ 5} \atop {y\ \textless \ -2}} \right. \left \{ {{y\ \textless \ -5} \atop {y\ \textless \ -2}} \right. y\ \textless \ -5</span>
21/х=49/7
49х=21*7
х=147/49
х=3
28:х=36:9
36*х=28*9
36х=252
х=7