Count checked Checkboxes with Rules

I have a commerce site which uses userpoints (=coins) for paying.

I have a special case - the product, which the user should buy with his coins, needs some fields filled out by the user. so I used a content type for this case and when he adds a new one 10 coins will be reduced from his account - this works already fine. now I have also a taxonomy in this content type and the user can add terms to it which are shown later in the form when he fills it.

Problem:
I need to count how many checkboxes of the taxonomy terms are checked and multiply the costs with them. so 3 of 5 are checked then 10 coins * 3 = 30 coins final price when he adds a new content type.

Is this possible with rules? I have no clue how to realize that
I´m front-end developer and no php coder.