Answer:
16
Step-by-step explanation: 
We can solve for a missing side using the Pythagorean Theorem 
a² + b² = c²
where a and b = the legs and h = hypotenuse 
Looking at the triangle created, we notice we are given a leg ( which has a measure of 12t ) and the hypotenuse ( which has a measure of 12ft ) 
That being said, we plug in what we are given into the Pythagorean theorem and solve for the missing side length ( aka b ) 
12² + b² = 20²
step 1 simplify 
12² = 144 
20² = 400
we now have 144 + b² = 400
step 2 subtract 144 from each side 
144 - 144 cancels out 
400 - 144 = 256 
we now have 256 = b²
step 3 take the square root of each side
√b² = b
√ 256 = 16 
we're left with b = 16 
So we can conclude that the length from the ground directly over point x to the stake is 16 feet. 
( important note: The Pythagorean theorem can only be used in right triangle. )