Answer: Mean
Step-by-step explanation:
Given that,
Initially there are four families and each of the family having an annual household income of $25,000.
So, mean in this case is $25,000
If a new family with an annual income of $75,000 moved in, then
Mean =

= $35,000
Therefore, mean changes from $25,000 to $35,000.
Both median and mode remains at $25,000 even with the addition of new family.
Hence, Mean would be mostly affected.