Adding a math equation to an API pull

Good afternoon,

I have a quick general question.

I have an API pull that shows a Calculation. In my case, the amount of carbon emitted. What I would like to do, is once the number is shown in the response field, I would like to multiply that number by the offset amount. Meaning, if there is 13 tonnes of carbon emitted by a person, I would like to have an additional field showcase 13x8.50=110.50. I would like to show just the $110.50.

Thanks for the help