An economy operates a progressive income tax system. The table below shows the annual gross income and the total income tax paid by an individual at different income levels:
| Annual Gross Income | Total Tax Paid |
|---|---|
| £45 000 | £5 400 |
| £60 000 | £9 000 |
| £75 000 | £13 500 |
| £90 000 | £19 800 |
| £105 000 | £27 300 |
What is the change in the average tax rate for an individual whose annual gross income increases from £60 000 to £90 000?
4%
7%
12%
18%
