pt prima parte;dai factor comun si tii cont ca a+b+c=7
a)2(a+b+c)=2*7=14
b)10a+10b+10c=10(a+b+c)=10*7=70
c)ax13+bx13+cx13+21=13x(a+b+c)+21=13*7+21=112
d)8a+8b+8c-12=8(a+b+c)-12=8*7-12=44
e)400-(5a+5b+5c)=400-5(a+b+c)=400-35=365
f)6a+6b+6c+100=6(a+b+c)+100=6*7+100=142