Answer: 13.5 inches
Explanation:
Let x be the length of the towel bar.
Since, the towel bar's ends from each end of the door are 7.75 each,
Thus, the width of the door = x + 7.75 + 7.75 = x + 15.5
But, According to the question,
The width of the door = 29 inches,
Therefore, x + 15.5 = 29
⇒ x = 13.5 inches