Boundary Value Analysis Without Single Fault Assumption

This is a past exam paper question and I am unsure of how to answer it:

How many test cases has your test suite for AlteredProduct? How many test cases
do you get, when the "single fault" assumption is dropped? Give a formula for the
number of test cases needed for a Computational Problem in n ≥ 2 variables, when
the “single fault” assumption is dropped.

I get what "single fault assumption" is but I don't know of a formula that would give me the number of test cases needed when n >= 2 and also how many test cases I would need when the "single fault assumption" is dropped.

AlteredProduct looks like this:

AlteredProduct:

Input: integers 1 ≤ x ≤ 10 and 2 ≤ y ≤ 12

Output: integer x ∗ y − 2

Give a test suite for boundary value testing

Thanks.