Question

Let's see who can crack this

5-4=23
8-1=63
6-16=32
9-9=78
3-9=6
3-81=?

Genius heads try this

Answer 1

(5)²-√4 =23
8²-√1 = 63
6² -√16 = 32
9² - √9=78
3² - √9 = 6

and 

3² - √81 = 0