Alissa cut a piece of string that was 17 feet long.
Darnell cut a piece of string that was 5 yards long.
We know that there are 3 feet in a yard, so to convert Darnell's string length into feet we just have to multiply it by 3.
(5) * 3 = 15 feet
Alissa wants to cut her string so that it was the same length as Darnell's.
We know that Alissa's string was 17 feet long, and that Darnell's string is 15 feet long.
17 - 15 = 2.
Therefore, Alissa should cut off 2 feet of her string.