Line Graphs with Percentages Data

I have data that looks like this (the data comes already summarized, I can't just use raw data and compute in BI):

I'm trying to create a line chart with year on the X axis, percent on the Y axis, and then different lines to show each of the three offices' results over time. But the problem is that the only way that I can get BI to have the percentage on the Y axis is to use "sum", which means if multiple offices are selected, it just adds up the numbers (instead of creating separate trend lines for each office).

Any advice on how to, in this example, have a line for each office on the same visual?