Assigning an inputs value to a dropdown option

Hello,

I am trying to create a dropdown list which has an input field next to it and have the data value of the dropdown option selected be equal to the input (percentages). Lets say the user needs to fill out a specific value from the dropdown list, I need the number that he inputs be tied to that specific value so that if he wants to do any calculations with that dropdown value, or just see the value of it later on he can do so.

Thank you in advance,
Luka