But my answer sheet ans is 2/5t(s-2/3t). May I know why? Thanks

We can leave the answers in many forms for this question, which is the reason why I mentioned earlier that my solution is just a suggested solution. : )

However, the answer 2/5t(s-2/3t) in the answer sheet is incorrect. There are many occasions where answers in the answer sheets provided is incorrect due to printing error, etc.

I have worked out another suggested answer (Answer (2)) in the next slide. Do take a look, and let me know if you have any question. Hope this helps! : )

Yes, I got the your answer 2. The answer sheet is incorrect. Thank you for helping me.

Welcome! Glad to help! : )