Answer: x=12.37 (2 decimal place) and the second box is √153
Explanation:
You would have to use pythagoras theorem.
The formula for the short side is x²=c²-b²
The formula with the numbers in it is x²=13²-4²
13²=169
4²=16
x²=169-16
x²=153
To find x on its own you would have to square root 153.
x=12.37 (2 decimal places)
Hope this helps :)