MARKING AS BRAINLIEST!! (Geometry)

Answer:
x = 15.49
Step-by-step explanation:
As you can see this is a right-angled triangle due to the right angle symbol, we can use Pythagorean theory to find the unknown length:
[tex]a^2 + b^2 = c^2[/tex]
In this case, we know C and B but not A so:
[tex]a^2 = c^2 - b^2[/tex]
Now plug the values in:
[tex]a^2 = 16^2 - 4^2[/tex]
[tex]a^2 = 256 - 16[/tex]
[tex]a^2 = 240[/tex]
Square root the answer to get A:
[tex]a = \sqrt{240}[/tex]
a = 15.49
x = 15.49
Hope this helps!