I did 4x10    30x9    21x5

the length of the golden gate bridge  1.7 mi (2.7 km) or 8,981 ft (2,737.4 m) 




It is made of steel

the length of the 

Manhattan Bridge 6,855 ft (2,089 m

            material : unknown

 the length of the Sydney Harbour Bridge

              

           1,149 m (3,770 ft)