In your last couple paragraphs, you want to include where you see the market for your book, and what would be competing titles. Also include any media contacts you may help that could help in the marketing platform for your book. Lastly, include your education, previous publishing history/credentials (if any), and background, as well as any other pertinent information that shows how or why you are qualified to write your book. Do not lie or even stretch the truth. Trust will be a key factor between you and your eventual agent.
Finally in closing your last sentence and ending salutation should be:-
“I would be happy to submit sample chapters, the synopsis, and the full manuscript for your further consideration. I hope you will be interested in pursuing MANUSCRIPT NAME, and I look forward to hearing from you soon.
DO NOT forget to check for typos (teh instead of the) and spelling or grammatical errors – those will only make a prospective agent press the delete button. Have someone proofread it for you – I remember an essay I wrote that was missing an “it” – which literally took me 13 times of re-reading before I was able to locate it.