To find the x, let's look at the sketch below:
All we simply need to do is to use Pythagorars theorem to find y
x is a radius and y is also a radius
Hence x and y are congruent
So Using Pythagoras theorem
y² = 3.6² + 4²
y² = 12.96 + 16
y² = 28.96
Take the square root of both-side of the equation
y ≈ 5.4
Therefore, x= 5.4