The mean age decreased.
I find it convenient to look at the additions with respect to the current mean age.
The current total age is 14×34. We have added members with ages (34 -10) and (34 +2), so the new total age is ...
... (34×14) + (34 -10) + (34 +2) = (16×34) - 8
Dividing this total by 16 will give the new mean age. (We already know it is less than 34.)
... ((16×34) -8)/16 = 34 - 1/2 = 33 1/2 . . . new mean age; a decrease