Question

What the perimeter of 2m 10cm and 45cm of a rectangle

Answer 1

Well if you divide 2 and 10 you get 5 and if you divide 5 and 45 you get 9 so the answer would be 59

Answer 2

You only told us the length of 3 sides, and from those 3,
we can already see that it's not a rectangle. (If you take
any 3 sides of a rectangle, two of them must be the same
length.)

So we have no way to tell the length of the 4th side, or to
add up the lengths of all 4 sides to get the perimeter.
It could be many different things.

The only thing we know for sure is that the perimeter must be
more than 2.55 meters. (That's the sum of the 3 sides you gave us.)