Final answer:
The cities at 10°E and 20°W on the equator are 30 degrees apart. This is calculated by summing the absolute values of their longitudes relative to the Prime Meridian.
Step-by-step explanation:
The question asks about the angle in degrees between two cities located at two different longitudes, 10°E and 20°W, on the equator.
Since longitudes are measured relative to the Prime Meridian, which is at 0°, and you can measure eastward or westward up to 180°, we need to find out the total separation angle between the two cities. The city at 10°E is 10 degrees east of the Prime Meridian, and the city at 20°W is 20 degrees west of it.
To get the total separation angle, you simply add the absolute values of their longitudes: |10°| + |20°| = 10° + 20° = 30°.
Therefore, the two cities are 30 degrees apart on the equator, which corresponds to answer choice (b).