1) 18х+30у+7х-5у= 25х+25у=25(х+у);
(х+у)=3; 25(х+у)= 25*3=75;
2) 84а+3b-73а+8b= 11а+11b=11(а+b);
(а+b)=7; 11(а+b)=11*7=77;
3) 3m+35n+24m-8n= 27m+27n= 27(m+n);
(m+n)=4; 27(m+n)= 27*4= 108;
4) 51c+85d+6c-28d= 57c+57d= 57(c+d);
(c+d)=2; 57(c+d)= 57*2= 114.