We can choose the first digit any of 3 ways  (3,4,or 5)

We can choose the second digit any of 5 remaining ways 
(we can choose any of the three {0,1,2} or either of the two of {3,4,5} that we 
didn't choose for the first digit.

We can choose the third digit any of the 4 remaining ways.

We can choose the fourth digit any of the 3 remaining ways.

That's 3*5*4*3 = 180 ways

Edwin