Make salary increase % and new actual salary both editable in compensation worksheet

Summary:

What is the best practice and solution to enable Line Manager to put in either a salary increase % or a new actual salary in the compensation worksheet?

Content (please ensure you mask any confidential information):

Normally, if you enable salary columns, once you insert a salary increase % in the worksheet, the new actual salary and salary increase amount will be calculated automatically to show the new actual salary. However, my client is keen to allow line manager to be able to update the new actual salary as well and the the salary increase % and increase amount will be calculated backwards based on the inserted new actual salary.