 
Norbert W. answered  07/11/16
Tutor
                    
        4.4
        (5)
            Math and Computer Language Tutor
The way the question is asked, since there are only 2 equations (x + 2y = 16 and 2x + y = 20) they would intersect in one point.
Let x = 16 - 2y => 2x + y = 32 - 4y +y = 20
                        => 3y = 12 => y = 4 and then x = 8
With these values, both greater than zero, then x + y = 12, which has to be maximum since there is only point that satisfies all the conditions.
     
     
             
                     
                    