The largest area of old-growth forest in the united states is located in

Tongass National Forest

Explanation:

The Tongass National Forest in Alaska is immense, and within it's nearly 17 million lies an area of old-growth that takes up 5.4 million acres in area. As the worlds largest old growth coastal temperate rainforest, the Tongass is irreplaceable.

reflecting point a across the origin negates both of its coordinates.

b = (5, -4)