Is 'timing' important in taxation? When is trading stock 'on hand' and why is this concept important? Illustrate your answer.

T opened a retail business in the 2019/2020 income year. During the income year he purchased 25,000 inventories from suppliers for $625,000 and sold 15,000 of them for $600,000. Calculate his taxable income for the 2019/2020 income year.