2: There are 3x 4y=a and 4x 3y=5.

So the band commutative 3x 4y=a, x=(5-3y)/4 gives 15 7y=4a, and a is greater than or equal to 15/4 because x.y is a nonnegative solution.

Ibid., 3x 4y=a, y=(5-4x)/3 gives 20-7x=3a, and a is less than or equal to 20/3 because x.y is a nonnegative solution.

Based on the above two points, a is greater than or equal to 15/4 and less than or equal to 20/3.

3. Incomplete conditions cannot be solved