Convert List<List<String>> to List<List<num>> in flutter

I would like to check a coordinate with in polygon (Google map). From my REST API, the polygon coordinates datatype was in List<List<String>>. I am using a specific package to check within polygon a package named poly which accept List<List<num>> datatype. To convert List<List<String>> to List<List<num>> for google map api in flutter, how should I do that?