Pretty sure the answer is B The horizontal asymptote y = 10 means that the final concentration will always be greater than 10%.
Explanation:
Since the 10 % solution that you're adding to the 30% solution is 10% acid when you add it to the 30 acid percent solution it would never decrease the acidity levels farther than 10 percent no matter how much you put because the solution your adding is at a 10% acidity and the other solution is 30% acidity and has a higher acidity level than the 10% so it could never go lower than the solution you are adding to it.
Really hope I did an okay job at explaining.