Okay. Follow this link, scroll down to "Image Height and Width Attributes."
FWIW, a width of 640 and a height of 480 is a good size. Small enough to be seen well but not so large it runs off the edge of the page.
Here's the img statement for your image above:
<img src="https://i.imgur.com/pccVWe9.jpg" width=640 height=480>
And here's how that looks:
