I think it’s 4.5 but I’m not sure

The closest answer would be B.

If you make it a triangle you’re going to be finding the hypotenuse. On the left the length is 2 and the bottom length is 4.

To find the hypotenuse the formula is a^2+b^2=c^2
2^2+4^2=c^2
4+16=c^2
20

Then you would find the square root of that which is about 4.5.