Răspuns :
a+b+c=18
2a+b+2c=25 => adunam cele doua relatii
____________
3a+2b+3c=43
2a+b+2c=25
a+b+c=18 => scadem cele doua relatii si rezulta
_____________
a + c = 7
(a+c)x(3a+2b+3c)=7x43=301
2a+b+2c=25 => adunam cele doua relatii
____________
3a+2b+3c=43
2a+b+2c=25
a+b+c=18 => scadem cele doua relatii si rezulta
_____________
a + c = 7
(a+c)x(3a+2b+3c)=7x43=301