In a proportional tax policy, each family would pay in proportion to how much they value the road. The total value is $900 (Huang) + $900 (Smith) + $700 (Hudson) = $2,500. So, each family's tax would be their value divided by the total value times the cost. For example, the Huang family would pay $900/$2,500 * $2,400 = $864. Each family would pay less than their value, so a proportional tax would pass.
In a headcount tax policy, each family would pay the same amount, which is the total cost divided by the number of families. So, each family would pay $2,400/3 = $800. This is more than the Hudson family values the road, so a headcount tax would not pass.
So, the answer is a. Only the proportional tax would pass.