A Space Probe Approaches a Planet,taking Measurements as It Goes $\vec { E }$

Multiple Choice

A space probe approaches a planet,taking measurements as it goes.If it detects a potential difference of 6000 MV between the altitudes of 253,000 km and 276,000 km above the planet's surface,what is the approximate electric field strength produced by the planet at 264,500 km above the surface? Assume the $\vec { E }$ field is approximately constant at these altitudes.

A) 261 N/C
B) 0.261 N/C
C) 561 N/C
D) 493 μN/C