Răspuns :

4a+4b+4c= 4(a+b+c)

a+b+c = 20+16 = 36 

4x36=144
4a+4b+4c=4(a+b+c)=4(20+16)=4x36=144
2a+2b+ca+cb=2(a+b)+c(a+b)=2x20+16x20=40+3200=3240