Query Code (newbie)

Hey everyone,

I know this is a very simple problem however I've literally just begun learning about SQL and this is the first ever code i've created using the language.

The error is:

Msg 102, Level 15, State 1, Line 30
Incorrect syntax near ')'. Located on line containing "create table Trailer_Type"

create table Tralier
(load_types varchar(20),
Serial_no varchar(5),
constraint trailerkey primary key(Serial_no));

create table Tractor
(Reg_no varchar(8),
Descript varchar(20),
constraint tractorkey primary key(Reg_no));

create table Unit
(Unit_no varchar(4),
Total_length int(3),
Max_load int(2),
constraint unitkey primary key(Unit_no));

create table Maintenance
(Reg_no varchar(8),
Date_in date(8),
Date_out date(8),
Descript varchar(20),
Job_no varchar(6),
Mech_name varchar(20),
constraint maintenancekey primary key(Job_no));

create table Load_type
(load_type varchar(20),
constraint typekey primary key(load_type));

create table Trailer_Type
(constraint holds foreign key (serial_number) references
Trailer(serial_no),
Constraint holds foreign key (load_type)
references Load_type(load_type));

I'd be very greatful if someone could help me.

Thanks

David