The change in distance is 30 because if you subtract both number you'll get 30
Answer:
"Why"
Explanation: A scientific law is a description of how the natural world behaves under certain circumstances.
The electric field strength is 
Explanation:
The strength of the electric field produced by a single point charge is given by:

where
is the Coulomb's constant
q is the magnitude of the charge
r is the distance from the charge at which the field strength is calculated
For the charge in the problem, we have:
is the charge

Therefore, the electric field strength is

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