Not knowing is not the problem
The instinct is to guess, or to freeze, and both cost more credibility than simply not knowing. What actually damages trust is pretending you have an answer you do not.
Say what you know, then commit to the rest
“I do not have that number in front of me, but I will confirm by end of day.” Naming what is missing and giving a specific timeline sounds more competent than a vague guess.
Redirect when someone else knows more
“That is a good question for [name], they know the details better than I do.” This is not dodging, it is routing the question to the most useful answer, which is exactly what a meeting is for.