1) при x+y=3;
6(3x+5y)+7x-5y=18х+30у+7х-5у=25х+25у=25(х+у)=25×3=75
2) при а+b=7
3(28a+b)-73a+8b=84a+3b-73a+8b=11a+11b=11(a+b)=11×7=77
3) при m+n=4
3m+35n+8(3m-n)=3m+35n+24m-8n=27m+27n=27(m+n)=27×4=108
4) при с+d=2
17(3c+5d)+6c-28d=51c+85d+6c-28d=57c+57d=57(c+d)=57×2=114