At what height from the surface of the Earth will the acceleration of gravity be four times less than on its surface?

Well, knowing how the gravitational acceleration was deduced, we will understand the solution.
In short, F = Gm1m2 / r ^ 2 = m1a (the mass m1 is incredibly small compared to Earth, so it is neglected)
Then a = Gm2 / r ^ 2 (this is a constant, and it is called the acceleration of free fall). And yes, this is the formula for the surface of the Earth (although even at the poles and at the equator there are different accelerations)
Accordingly, in order for the acceleration to decrease by 4 times, the denominator must be increased by 4 times, that is, the distance will grow to the root (4), this is 2 times