Your inequalities are


      x +    y >= 15      (1)

   170x + 270y <= 4000    (2)

      x >= 0, y >= 0      (3)


where x = kilos of bangus and y = kilos of pork.


In visual form, this inequalities are shown in the figure below



    


                        Plot x + y = 15  (red line), 170x + 270y = 4000 (green line)



We consider the quadrant QI, since we have these inequalities (3).


The solution set is ABOVE the red line (including points in this line) and below the green line (including points in this line).


You may use any point from this set as a solution.


For example,  x= 10 (kilos of bangus)  and  y = 8 (kilos of pork).

              Check.  10*170 + 8*270 = 3860 (which is less than 4000).


And more than million other different solutions . . .