What should the number be in the lower right corner?

The answer is 6

Step-by-step explanation:

If you can see the top first digit is the product of top second digit and bottom number,

i.e.,

63.) 6 = 3 × 2

42.) 4 = 2 × 2

82.) 8 = 2 × 4

So,

61.) 6 = 1 × 6

Thus, The answer is 6

-TheUnknownScientist 72