Trouble with calculations within the form

In this form, I am attempting to have >1 set of checkboxes, with each item adding to a total.  I then want to multiply that total by one of two numbers based on a different radio button. 

Example:

checkbox set 1 has 5 of 7 boxes checked == 7;
checkbox set 2 has 3 of 7 checked == 3;
checkboxes 3 and 4 have nothing checked == 0 each;
Total == 10, multiply that by 220 or 305 based on radiobutton 1
  The goal here it reflect two sets of prices (member vs. non-member)

I originally set up 4 checkboxes where the values == 1 for every item then had the calculation field look like:
(cb1 + cb2 + cb3 + cb4) * (radiobutton value)

I kept getting gibberish, so I decided to see if the (cb1 + ...cb4) worked.  No - in the calculation field, I get things like "3+1+1+1" instead of "6".  Reading the help implies that the calculation isn't completed until every field in the calculation has a value, so I added a "None" to each item (except the first), preselected with a value of zero.  I still get 3+1+0+0, etc. 

Help, please.  Thank you.

Thank you for contacting us.

For some reason, the plus signs are not interpreted correctly on your Form Calculation field. Please re-add the + symbols in order to fix this.

If you need any further assistance, please let us know. We will be happy to help.