.
The analysis in the post by @CPhill is either incomplete or incorrect.
Below I explain WHY it is so.
If to accept interpretation of the problem as in the post by @CPhill,
then the problem is
maximize 12800x + 8400y under these constraints
6x + 7y <= 42
4x + 3y >= 48
x >= 0, y >= 0.
But the feasibility domain under these constraints is .
Indeed, it is obvious that in positive domain for x and y
4x + 3y < 6x + 7y.
So, if (x0,y0) is the point in the feasibility domain, then
48 <= 4x0 + 3y0 < 6x0 + 7y0 <= 42,
and we arrive to the absurdist inequality 48 < 42.
This contradiction disproves the existence of solutions.
So, the answer for this analysis is that the given problem HAS NO solution.
There is EMPTINESS at this point.