Answer: 66 possible combinations.
Step-by-step explanation:
To have a positive product we have 3 situations.
The 4 numbers are positive:
if the "order" of the selection does not matter, then we have only one solution here:
1, 2, 3 and 4.
Second case, we have two negative numbers and two positive numbers.
Here we can use the fact that in a group of N objects, the number of different combinations of K objects (where K ≤ N) is:

Here we have 5 negative numbers and we want to make groups of 2, so the possible combinations are:

And we have exactly the same for the other two positive numbers, but in this case we have N = 4 and K = 2.

The total number of combinations is the product of those two:
C = 10*6 = 60 combinations
Now, the last option is that the 4 numbers are negative numbers, so here we have 5 negative numbers and we want to make groups of 4.

So in total, we have: 1 + 60 + 6 = 66 possible combinations.