Which statement best describes the interquartile range of this set of weights?

{120 lb, 115 lb, 135 lb, 105 lb, 80 lb, 160 lb}
the difference between the first and sixth elements of the set as it is written above
the difference between the second and fifth elements of the set as it is written above
the difference between the first and sixth elements of the set after it has been ordered from least to greatest
the difference between the second and fifth elements of the set after it has been ordered from least to greatest