That function was added in version 8, so it's not present in version 7.
The low-tech option is to add something like a free-format question to each page and manually type it in.
The high-tech option is to write a script that counts it up for you. For example, the PageNumber function returns what page you are on. If your CBC exercise starts on page 10, then you could do something like this: [%PageNumber() - 9%] of 12. PageNumber() evaluates to 10, then 9 is subtracted from it and the net results is 1 of 12 on the page. When the person goes to the next page, PageNumber() evaluates to 11, and 11-9=2, so you get 2 of 12, and so forth.