The rope tied to the tree will make a triangle.
The height of the triangle = 180cm
The base of the triangle = 200cm
to find how much rope you need, work out the hypotenuse using Pythagoras:
180^2 + 200^2 = 72400
√72400 = 269.0724809
This is the length of rope he needs, however you need to +30 as this is what he will need when he ties the rope:
269.0724809 + 30 = 299.0724809
299.0724809 is less than the 270cm of rope he has, so he would need more.