Will your json have this stucture 1,2,3,… etc ? What will happen if value is 2.9 below value again will be 2 and above 3? What will happen if number entered is not in list ?

Logic No.1
If the user entered VA = 2
Then Result need to come= 0.079 (This Value is VB)

Logic No. 2
If the user entered VA = 2.9 (Note: This value is not available in the sheet, but we need to find out the nearest lower value of 2.9 which is 2 & nearest higher value of 2.9 which is 3)

If I achieved to get lower and higher values then I have a formula to get the value of VB

First case check if number entered in textbox is integer, then if true check if is in list VA, and if true then select item in list VB index number’s index in list VA

If number is not integer, split at . and get first item in list, check it that number is in list VA, check if that number plus 1 is in list VA, then set lower value to that number and higher to number +1

Please note that I have some data like below then I am unable to do as @dora_paz said. Because All VA values are not an integer. and also every time VA value not increasing +1
Then How Can I do that.