It looks like the values are already in some other msg property. Use the copy path button to grab the path to the value and use that with
msg. instead of
env.get (env.get is for environment vars not for accessing msg properties)
There’s a great page in the docs that will explain how to use the debug panel to find the right path to any data item.
Pay particular attention to the part about the buttons that appear under your mouse pointer when you over hover a debug message property in the sidebar.
Ps, it may be necessary to use parseInt or parseFloat to coerce the string values into numbers before doing math operations.