Metres are exactly 100 cm in length, the easiest way to go from metres to centimetres is to simply add the extra 1 or 2 zeros, so 4.5 metres would be 450 centimetres.
As for the millimetres, 1mm is equal to 0.1cm, once again, just move the decimal forward by one numeral, and you'll have the converted value, making 50mm = 5.0cm.
Your shark would be 450cm long and have teeth with an average length of 5cm.
