How can we execute workflow by definition Id from Activity

[kpatelghd]

Hello,
I have one root workflow that accepts JSON data with list of Workflow definition Id and input data. And it calls one Custom Activity that I build. Now, I want to execute workflow based on definition Id that I got in JSON and also pass the required input to it that I received via JSON input in root workflow too. How and what is the best way to achieve this. Please note that I do not have API end point trigger for all the workflow except for the root workflow. And, I want to achieve this from inside Custom Activity itself.