Find the distance from P to Q in km. P: 40°N, 45°W. Q: 35°N, 45°W.

First, let's identify the coordinates of the points:
Point P: $40^\circ N, 45^\circ W$
Point Q: $35^\circ N, 45^\circ W$
Point T: $35^\circ N, 135^\circ E$

We will use the following standard values:
Radius of Earth, $R = 6370$ km
1 nautical mile (nm) = 1.852 km
1 degree of latitude or great circle arc = 60 nautical miles
1 degree of latitude along a meridian $\approx 111$ km

a) Find the distance from P to Q in km.