​Rob's income rises from $50,000 to $60,000 and his income tax increases from $6,000 to $7,500.His marginal tax rate is 12.5%.

The marginal tax rate is calculated by dividing the change in tax by the change in income. Here, the change in tax is $1,500 ($7,500 - $6,000) and the change in income is $10,000 ($60,000 - $50,000). So, the marginal tax rate is $1,500 / $10,000 = 0.15 or 15%.