Question 1048272
C=chicken
P=pigs
C+P=25.  First add the variables. 
2C+4P=70 Then associate the variables with the number of legs and add.
multiply the first by -2 then add, to eliminate C.
-2C-2P=-50
2P=20
P=10
10 pigs with 40 legs
15 chickens with 30 legs.