Answer:
x = 21 units
Explanation:
The tangent squared is equal to the secant's total length multiplied by the secant's length without the part inside the circle.
So here, that will look like: 36² = 27 * (27 + x)
Expansion and multiplication gives us: 1296 = 729 + 27x
Subtract from both sides: 567 = 27x
Divide from both sides: x = 21.