You are on the right track with the acid - it is fully dissociated so if you know the pH, you should know the

concentration in solution B.

You also obviously know what the [Pb] is in solution A.

The volumes come into play in that when you mix the two solutions, the concentrations of each species in the mixture will change compared to what they are in the isolated solutions before mixing.

So, let's assume you take 1 L of solution A and 2 L of solution B, and mix them. We can figure out the concentrations of each ion is in the new mixed solution by calculating the number of moles of each ion in each solution (which we can do because we know the volumes), then divide by the new volume in the mixture to determine the final concentrations. With this, you should be able to apply the Ksp condition to determine if there is a precipitate.

Note: you will get the same answer if you put in 2 L and 4 L, or 4 L and 8 L... or generalize the relative concentrations. But putting in specific values can make solving the problem a little more straightforward.