How to dynamically move text layer based on the width of another text layer

Hi, I have to admit I don't have a head for expressions and find SourceRectAtTime() difficult to wrangle. I have been on the various forums trying to figure this out using other people's expressions to no success. 

I'm creating a location marker for a show using two layers of right-aligned text that are positioned in the bottom right of the screen. I want the first layer (currently "San Fransisco") to remain fixed to the right, while the second layer (currently "Chinatown,") will move dynamically when the first text layer is modified. Both need to remain right aligned as they're typed out. 

Would greatly appreciate any help, thank you.