Checkbox game sum points in shopping list

I am making a game where you have "good" products and "bad" products. For each good product that you pick you win one point and for each bad product you lose one point. I want them all sum up once you click the button "comprar! aka Buy!)

I tried with different blocks but it never adds up correctly.

This is how the front page looks like. Product one, two and six are good ones and the rest are bad ones.

And the blocks are these ones:

Can someone help me in understanding what is wrong?

Use for each item in list 'every checkbox'. And for each item check if it is in good list (+1) or in bad list (-1).

it still adds weird numbers...


1 you need to set score to 0 everyone time click button.

2 if checkbox is checked,
then ( if it's in good list,
add 1 to score,
else add -1 to score. )

Try something like this: