a) 2a+2b+2c=
=2•(a+b+c)
=2•7
=14
b)10a+10b+10c=
=10•(a+b+c)
=10•7
=70
c)a•13+b•13+b•13+21=
=13•(a+b+c)+21
=13•7+21
=91+21
=102
d)8a+8b+8c-12=
=8•(a+b+c)-12
=8•7-12
=56-12
=44
e)400-(5a+5b+5c)=
=400-[5•(a+b+c)]
=400-(5•7)
=400-35
=365
f)6a+6b+6c+100=
=6•(a+b+c)+100
=6•7+100
=30+100
=130