Compute the assessable income for the relevant years of assessment.

The basis period for YOA 2009 is the 12-month accounting period ending in the preceding tax year (2008).

$$\text{Assessable Income (YOA 2009)} = \text{Profit for period ending 30 June 2008}$$ $$\text{Assessable Income (YOA 2009)} = 280,000$$

The basis period for YOA 2010 is the 12-month accounting period ending in the preceding tax year (2009).

$$\text{Assessable Income (YOA 2010)} = \text{Profit for period ending 30 June 2009}$$ $$\text{Assessable Income (YOA 2010)} = 459,000$$

The new accounting date is 30 September. The first accounts prepared to the new date are for the 15-month period ending 30 September 2010. This date falls in the tax year 2010, so YOA 2011 is the year of change.
For the year of change, the basis period is the 12 months ending on the new accounting date in the preceding tax year. This means the 12 months ending 30 September 2010.
The profit for the 15-month period (1 July 2009 to 30 September 2010) is 362,000.
We need to apportion this profit to get the profit for 12 months.

$$\text{Profit per month} = \frac{362,000}{15}$$ $$\text{Assessable Income (YOA 2011)} = \frac{362,000}{15} \times 12$$ $$\text{Assessable Income (YOA 2011)} = 289,600$$

The basis period for YOA 2012 is the 12-month accounting period ending in the preceding tax year (2011), which is the period ending 30 September 2011.

$$\text{Assessable Income (YOA 2012)} = \text{Profit for period ending 30 September 2011}$$ $$\text{Assessable Income (YOA 2012)} = 330,500$$

The basis period for YOA 2013 is the 12-month accounting period ending in the preceding tax year (2012), which is the period ending 30 September 2012.

$$\text{Assessable Income (YOA 2013)} = \text{Profit for period ending 30 September 2012}$$ $$\text{Assessable Income (YOA 2013)} = 324,000$$

Summary of Assessable Income:

• YOA 2009: $\boxed{280,000}$
• YOA 2010: $\boxed{459,000}$
• YOA 2011: $\boxed{289,600}$
• YOA 2012: $\boxed{330,500}$
• YOA 2013: $\boxed{324,000}$