Answer: 20000
Let person B’s income be , so person A’s is . Consider where the incomes fall relative to $30,000.
If both incomes are at most $30,000, both taxes are and A’s tax is only times B’s, so this case is impossible.
If , B’s tax is and A’s tax is :
so and , which is in this case.
If , B’s tax is :
so and , which is also in this case.
The possible incomes of B are $20,000 and $45,000, so the least possible income is $20,000.
Check: For : B pays , and A, with income , pays .
Watch for: The most common wrong value is , which assumes both incomes are above $30,000; check every placement of the two incomes relative to the bracket boundary.