
Answer:
3. $20,000
Explanation:
Given,
Net worth increase = $100,000,
Since, Net worth increase + living expenses = income,
If there are no living expenses,
Net worth increase = income
Thus, income = $100,000,
Now, income = income from unknown sources + income from known sources,
We have, income from known sources = $80,000,
By substituting the values,
$100,000 = income from unknown sources + $80,000,
⇒ Income from unknown sources = $100,000 - $80,000 = $20,000
Hence, option 3 is correct.