The table below shows the annual income tax paid by households in an economy at different levels of gross annual income.
| Gross Annual Income | Total Income Tax Paid |
|---|---|
| £20,000 | £1,200 |
| £35,000 | £3,900 |
| £55,000 | £9,900 |
| £80,000 | £19,900 |
| £110,000 | £34,900 |
What is the marginal rate of income tax when an individual's gross annual income increases from £35,000 to £55,000?
11%11\%11%
18%18\%18%
30%30\%30%
40%40\%40%
