Reducing 3 SQL Transactions To Just 1

Hi guys, how are you?

Ive got a little question, i hope you can help me up

in sql server i have 3 tables


Code:

user
id_user - autoincremental int, primary key
username - varchar 30

car
id_car - autoincremental int, primary key
carName - varchar 30

user_car
id_user - int, foreign key
id_car - int, foreign key



what i want to do, is to
1.- insert a row in User,
2.- insert a row in Car
3.- using SCOPE_IDENTITY, to insert a new row in user_car that relates the ids of the last added car with the last added user.

But i need that to be done in one single transaction.
Once that is done, i have another question

how can i do the same but where i can add a variable number of different cars? in other words, i add 1 user and then add 5 cars, then create 5 rows in the user_car where i have the id of the last added user with the incremental id of the last 5 added cars

how can this be done in one single transaction, i cant make it in 3 transactions cuz it would cause me a lot of trouble. Any help?

my transaction should be something like this


Code:

insert into user(username) values('user1');
insert into car(carName) values('car1');
insert into user_car(???,???)




but im not sure how to do this in one single transaction