2,150mm.
Step-by-step explanation:
Let’s take away the “mm” and “cm” for now. Since 10mm = 1cm, it’s basically multiplying by 10 to the number or adding a 0 behind the number. This means that if you take 215 cm and multiply it by ten, you will get the number 2,150, which is the mm equivalent of 215 cm. You can also use this for many other equations. This is called conversion.
Hope this helps you understand!