To find the range, first order the data from least to greatest. Then subtract the smallest value from the largest value in the set.
In this problem is it a little complicated because you have to do it in two steps.
Stem 5 Leaf 4 5 (5-4 = 1)
Stem 6 Leaf 0 6 9 (9-0 = 9)
Stem 7 Leaf 2 3 4 5 5 (5-2 = 3)
Stem 8 Leaf 1 2 8 9 (9-1 = 8)
Stem 9 Leaf 5 6 (6-5 = 1)
So, now we have:
51
69
73
88
91
So we subtract 91-51 = 40 which is your answer.
Hope this helps.