Celina measured the height of a window frame as 5.55 feet, but the actual height was 6 feet. What is the percentage of error in Celina's measurement?
To find the percentage of error, we need to determine the difference between Celina's measurement and the actual height, and then divide that by the actual height.
The difference between Celina's measurement and the actual height is 6 - 5.55 = <<6-5.55=0.45>>0.45 feet.
The percentage of error is then (0.45 / 6) * 100% = 0.075 * 100% = 7.5 %. Answer: \boxed{7.5}.