Question

I a+b=20
  b+c=30
  3*a+7*b+4*c=?

II a+b=33
   a+c=11
   5*a+3*b+2*c=?

Answer 1

I. 3*a+7*b+4*c= 3×20+4×30= 60+120= 180 II. =3×33+2×11= 99+22= 121

Answer 2

3a+3b+4b+4c=3(a+b)+4(b+c)=3*20+4*30=60+120=180

3a+2a+3b+2c=3(a+b)+2(a+c)=3*33+2*11=99+22=121