You should not be using an external speaker when doing web conferencing. This could result in echoes or loud feedback when sound from the speaker gets picked up by the external microphone.

Getting a headset would be the cheapest option in solving this problem. A good headset should be able to pick up your voice only and not the surrounding noise. You will need to spend more that a hundred for a good set.

Going to need more information than that in order to figure out a proper solution.

Is the speaker there just for you to listen in on zoom or is it for the entire class as well?

When teaching, are you standing/sitting fixed at a specific location or will you be moving around a specific area? This will determine whether you need a wired or wireless headset. This will also determine whether you can use a simple webcam or something more complicated.

Will you be using some kind of whiteboard that need to be visible to those using zoom? A simple webcam may not be sufficient in this situation.

The more complicated it gets, the more likely that you will need an assistant to handle the extra stuff while teaching. Also the hardware cost will go up as well.

That is the point. You don't want sound from the external speakers ending up in the microphone. Microphones generally don't work well in noisy environment. Your external speaker is essentially a source of noise in this situation.

How many thousands of ringgit are you prepared to spend on this? You are essentially looking for a video conferencing kit for a large room. Specialized microphones and speakers with noise cancelling features.
https://www.logitech.com/en-my/products/video-conferencing/room-solutions/rally-ultra-hd-conferencecam.html