18.
a) a+b=20
b+c=30
3a+7b+4c=
=20*3+30*4=
=60+120=
=180
b)a+b=33
a+c=11
5a+3b+2c=
=33*3+11*2=
=99+22=
=121
19.
x+3y=2y+z=14
a) x+5y+z=
=14+14=
=28
b)3x+15y+3z=
=14*3+14*3=
=42+42=
=84
c) 5x+11y+2z= asta nu stiu sa o fac (imi pare rau)
d)5x+19y+2z=
=14*5+14*2=
=75+28=
=103