yett | small webpage library to control the execution

Ey, I have a total value ouput and I wanted to add a function that's linked to it. But I'm having issues putting it together. I just get NaN or the "not defined" error in the console.

The function I want to use for the total value output:

I have an checkbox and an total value, I want the total value to decrease when checkbox is unchecked, and when its checked again it needs to go to the standard value.

When the checkbox is unchecked I want the total value to go -300, and when its checked again it removes the -300, so its back to normal. But my code doesn't work. It just doesn't do anything.

I have a total value(720), and a selector that has values, and when you select 1 thing it adds to the 720 so for example I get 740. But if i select something higher or lower it adds to the 740 and not the 720. I found stuff about updateTotal. But I just fooled around with that and couldn't get it to work.

So I hope someone could show me how this can be done. Thanks :)

My html value output:

I have a script that sums 2 values. And im planning to add more values, but first I need to get it to work. People told me to give them the NUMBER value, so I did but now it doesnt even give an output.

Okay, so I have an output of a value that changes on basis of what you select. But I want to have the text "Total €" in front of it like:

.

But my output now is:

.

And I would also like to change the "." in the value to a ",". But every time I add something at places the blocks overlap each other etc. So I hope you guys have some solutions/ideas.

My html/Styling of the value output: