Answer:
30 feet
Explanation:
You want to know the distance between the first and last of 10 stakes evenly spaced, such that the first and fourth are 10 feet apart.
Gaps
Between stakes 1 and 4 are 3 gaps. Between stakes 1 and 10 are 9 gaps, which is 3 times as many.
The distance from the 1st to 10th stakes will be 3 times the 10 ft distance from the 1st to 4th stakes.
3 · 10 ft = 30 ft
The first and tenth stakes are 30 feet apart.