Redistimeseries how to reference query A to do math expression

I’m pulling redistimeseries with TS.GET to get the latest value of a key into grafana. This is query A. It return the latest time value such as time: 11/22/2022, value: 30. Now, what I want to do is reference this value of 30 and do a simple math expression, so I add an Expression, call it B, and in the Operation, I select Math, and in the Expression, I put $A*2. I want for expression B to return 60, but it doesn’t. It actually shows no data in the table. How do I specify an expression to do simple math on a redistimeseries query?