Jerry, edit your post to remove your email address. Very dangerous to post such private information in a public forum. Click the three vertical dots to the right of your post and select Edit reply.
So, do you need an Ethernet cable (the network connection) or a HDMI cable (connects the Roku to the TV)? Mentioning the USB port is confusing your post, because the only thing the USB port is used for is playing media from a connected storage device, such as a USB stick. When you use the word "adapter", we don't know exactly what you're looking for. If you don't have an HDMI capable TV, and you're looking for an HDMI to Analog cable (which your Roku 3 did not come with), that requires a converter, not an adapter.
To be honest, it may be cheaper to just buy a new Roku. The Roku 3 is rather outdated and slow and will probably lose support soon. If you set it up using the same Roku account, all your channels will be installed. Depending on the service, you may not even need to log into some of them if you were already logged in on the old one. All you need to do is rearrange the icons the way you want, and maybe make adjustments to various per-device settings.
