It's a pleasure &With pleasure的区别

(1)Thank you for helping me.
It's my pleasure
(2)Would you please open the widow?
With pleasure.
可见It's my pleasure是回答别人的感谢的,可译为“那是我应该做的”,而whth pleasure是回答别人的请求的,可译为“好的,乐意效劳”.
第一句是谢谢的意思.