Zhang's family has eight members and earns $80,000 per year. Suppose that there is a $4,000 exemption per family member and that the following are the income tax rates that are applicable: 10% on the first $10,000 of taxable income, then 15% on the next $20,000, then 20% on the next $30,000, and 30% on all taxable income above $60,000. What is Zhang's family's average tax rate