Identify the leaf of 42|3 if the key is 13 17 =137

Answer: Choice A
Explanation:
The format is [tex]\text{stem} \big| \text{leaf}[/tex] when writing the key. The leaf is always on the right hand side. So for [tex]42 \big| 3[/tex] we have a stem of 42 and leaf of 3 forming the number 423.
As another example, something like [tex]58 \big|9[/tex] has a stem of 58 and leaf of 9 to form the number 539.