Answer:
D. 21 ft
Step-by-step explanation:
We need to use Power of Points, which basically says that for intersecting chords in a circle (see attachment), a * b = c * d.
Here, we can say that a = x, b = 6, c = 7, and d = 18. Then, we have the equation:
ab = cd
x * 6 = 7 * 18
6x = 126
x = 21
Thus, x is 21 ft.
Hope this helps!
