# How to adjust a cash transfer program's income requirements for inflation?

For a study, I would like to "estimate" the income requirements for a cash transfer program on 2018 based on information from 2015. This cash transfer program has two income lines that it uses to determine who is eligible to receive the benefits. People whose income is below the first line receive more benefits, people who is below the second line but above the first one receive some benefits, and people with incomes above the second line are not eligible. The information that I have is the following:

Income_Line_One_2015 = A, Income_Line_Two_2015 = B

Income_Line_One_2018 = C, Income_Line_Two_2018 = ?

I tried using the official inflation rate published by my country's government for the period 2015-2018, but the result didn't seem appropriate. What I did was:

B*(1 + IR/100)

I don't know if this is the correct way to use it.

I even tried this to see if it yielded a result that "looked better" than the previous one:

 Income_Line_Two_2018 = B*(C/A)

Concretely, my question is: is there any way to correctly estimate the value I am looking for using only the information that I have available?

Thank you