Image of App

I am trying to subtract (mathematics subtraction) 2 string values which I am getting from the Firebase and i want it to be displayed at my ListTile (Under Total In Service). The values are: -

1. Total Equipment (80.0)
2. Total OOS (20.0)

and I should get Total In Service = 60.0.

Instead I get a String value displayed as Total In Service: 80.0 - 20.0.

Here are the codes: -

Row(
children: const [
  Padding(
    padding: EdgeInsets.fromLTRB(0.0, 30.0, 0.0, 0.0),
  ),
],

), Row(children: [ Expanded( child: SizedBox( height: 400.0, child: FutureBuilder( future: users.doc(widget.value2).get(), builder: (context, snapshot) { if (!snapshot.hasData) { return const CircularProgressIndicator(); }

              Map<String, dynamic> data = snapshot.data!
                  .data() as Map<String, dynamic>;

              return ListView(
                children: [
                  ListTile(
                      title: const Text('Comments:'),
                      subtitle:
                          Text('${data['Comments']}'),
                      trailing: SizedBox(
                        width: 100,
                        child: Row(
                          children: [
                            IconButton(
                                icon: const Icon(
                                    Icons.edit),
                                onPressed: () {
                                  _updateComments();
                                }),
                          ],
                        ),
                      )),
                  ListTile(
                      title: const Text(
                          'Total Equipment:'),
                      subtitle: Text(
                          '${data['Total Equipment']}'),
                      trailing: SizedBox(
                        width: 100,
                        child: Row(
                          children: [
                            IconButton(
                                icon: const Icon(
                                    Icons.edit),
                                onPressed: () {
                                  _updateTotalEquipment();
                                }),
                          ],
                        ),
                      )),
                  ListTile(
                      title: const Text('Total OOS'),
                      subtitle:
                          Text('${data['Total OOS']}'),
                      trailing: SizedBox(
                        width: 100,
                        child: Row(
                          children: [
                            IconButton(
                                icon: const Icon(
                                    Icons.edit),
                                onPressed: () {
                                  _updateTotalOOS();
                                }),
                          ],
                        ),
                      )),
                  ListTile(
                    title:
                        const Text('Total In Service'),
                    subtitle: Text(
/*