in a school book which has an example application letter it says the following:
I am certain I can help improve your accounting functions while increasing your company's bottom-line profitability.
If I were to write this sentence, I would probably write this:
I am certain that I can help to improve your accounting functions while increasing your company's bottom-line profitability.
(note I added 'that' after certain and 'to' after help)
Thank you.