Question

a+b=21 si b+c=30,sa se calculeze:
a+2xb+c
c-a
2xa+3xb+c
a+4xb+3xc

Answer 1

a+b=21
b+c=30

a+2b+c= (a+b) +( b+c)= 21+30=51

(b+c) - (a+b)= b+c -a-b=c-a= 30-21=7

2a+3b+c= 2a+2b+ b+c= 2*(a+b)+(b+c)= 2*21+30=42+30=72

a+4b+3c =a+b+ 3b+3c= (a+b)+3*(b+c)=21+3*30=111

Answer 2

a+2xb+c
a+b=21   b+c=30
a+b+b+c=21+30=51

2xa+3xb+c
a+b=21   b+c=30
2a+2b+b+c=2(a+b)+30=2x21+30=72

a+4b+3c
a+b=21  b+c=30
a+b+3b+3c=21+3(b+c)=21+3x30=111