You can rest assured. I'll make it.

你尽管放心，我会成功的。

I could do that even with my eyes closed.

我闭着眼睛都能做那件事。



I'm an old hand at this.

我是这方面的老手了。



I'm certain of my success.

我肯定会成功的。



I'm a hundred percent certain.

我有百分百的把握。



I'm confident in my ablity.

我对自己的能力很自信。



I bet I'll get the first prize.

我打赌我会得一等奖。



I'm absolutely sure I'll pass the exam.

我绝对相信自己能通过考试。