VirtualBox Windows 7 32 or 64 bit?

Which version should I use so that I have more performance?

Unfortunately have a relatively weak notebook…

That depends on which architecture your processor has and which supports the operating system. With the key combination Windows key + Pause you see under "System type", which system you have.

Have a 64 bit laptop with linux mint 19.2, but need school for visual basic 2010.

If the laptop has 64-bit, then take 64-bit.

Greetings to your teacher - you're obviously a decade ahead of the school plan. But yes you can also use age old 32bit operating systems under a Virtualbox 64bit.

At less than 4GB RAM the 32bit version, at 4GB RAM or more the 64bit version.

P.S. From 2020, the support of Windows 7 will be completely discontinued. But you can still upgrade to Windows 10 for free if you have a valid Windows 7 license. It works like this:

Use this tool to read the Windows 7 Key and note it down: https://www.downloads.focus.de/app/windows-8-product-key-viewer

Download the Media Creation Tool from the Microsoft website. So you can create a Windows 10 USB bootstick.
Simply boot the created stick and follow the instructions of the installer. It offers the possibility to completely delete the hard disk. During the installation the notebook will be restarted several times.
After completing the installation and the first start, the setup wizard appears. He sets up the WLAN and offers the possibility to create a Microsoft account. You should do that if you do not have one. Otherwise log in with your Microsoft account.
Activate Windows 10 with the noted Windows 7 Product Key. The activation will then be permanently saved in your Microsoft account. If you have to reinstall Windows 10, it is enough to log in again with the Microsoft account. Windows 10 will be activated again automatically. Entering the product key is no longer required.

Then you should disable all unnecessary desktop effects on weaker devices. Then Windows 10 runs even on weaker devices afloat.