The magnitude of the Earth's acceleration is 
Explanation:
First of all, we start by calculating the magnitude of the force exerted by the apple on the Earth. According to Newton's third law, this is equal to the force exerted by the Earth on the apple, which is the weight of the apple, given by:

where
m = 0.43 kg is the mass of the apple
is the acceleration of gravity
Substituting,

Now we can find the Earth's acceleration by applying Newton's second law:

where:
F = 4.2 N is the net force exerted by the apple on the Earth
is the mass of the Earth
a is the Earth's acceleration
And solving for a, we find:

Learn more about Newton laws of motion:
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