Try downloading an app if the phone is not doing it.
Define variables
left is l
right is r
Ask input
left or right
Ask input value
Equate l or r to the input value
Show ladder with steps equal to input value and in the side of input variable
Answer:
Computer keyboard,Microphone,Image scanner,Touchscreen,light pen
Explanation:
sorry that all device i know
It can be any letter or number as long as its validated.