Answer: 5
Explanation:
This is something you could do by trial and error.
The visible numbers are 1,2,3,4,6 which multiply to 144.
Another approach is to notice that 5 is not a factor of 144, so it must be the hidden value not part of the items multiplied.
Every other number 1,2,3,4,6 is a factor of 144.
1*144 = 144
2*72 = 144
3*48 = 144
4*36 = 144
6*24 = 144
