How tall is the table?

A building is being prepared for opening. People are decorating the building with 12 flags. At first they arrange the flags 4 to a side, as shown, but then they see that the flags can be arranged 5 to a side using only 12 flags. How?
Below is a little math equation, made of matchsticks, that does not add up. Can you move just one match stick and fix the equation?
Can you crack the unlock code for the lock using the 5 clues below?
682
– One number is correct and well placed614
– One number is correct but wrongly placed206
– Two numbers are correct but both are wrongly placed738
– None of the numbers are correct780
– One number is correct but wrongly placed