Container A holds x liters of water.
Container B holds 2391 liters of water more than container A, so container B holds x+2391 liters of water.
Container A and B hold 11875 liters of water altogether.
[tex]x+x+2391=11875 \\
2x+2391=11875 \\
2x=11875-2391 \\
2x=9484 \\
x=\frac{9484}{2} \\
x=4742[/tex]
Container A holds 4742 liters of water.