Answer:
It's 16m 
Explanation:
Let's say the missing side is C, and since the triangle is right-angle triangle, you can use Pythagoras theorem. Which is 
 C squared is equal to A squared plus B squared 
Like this: c^2 = a^2+b^2
Then
 c^2= (10)^2 + (12)^2 
c^2= 100 + 144 
c^2= 244
c= 

c = 15.6 
 Hope this helps :)