Accounting for profit/loss for disposal

Hello sir, I need help with this case the teacher's solution says one thing and mine says another I've been stuck on it for 5 days and my exam is on the 27th would you please show me the correct method of handling this case out cuz its driving me mad thank you very much sir I appreciate it btw his answer was 625 profit mine is 3500 loss A business has an accounting year end of 31 March. It purchased a truck on 1 April 20X3 at a total cost of $21,000, including $1,000 for one year of insurance cover. At the date of purchase, the truck had an estimated useful life to the business of eight years, and had an estimated residual value of $3,000. The truck was traded in for a replacement vehicle on 31 March 20X8 at an agreed valuation of $10,000. The truck was depreciated on a straight-line basis, with a pro-rated charge in the year of acquisition and disposal. Calculate the profit or loss on disposal of the truck.