The expression of the electric flux is

Here,
Q = Total charge enclosed in the closed surface
= Permittivity due to free space
Rearranging to find the charge,

Replacing with our values we have finally



The charge enclosed by the box is 0.1684nC
The sign of the charge can be decided by using the direction of the flux. The charge enclosed by the cube can be calculated by using the electric flux and the permitivity of free space.
Taking into account the rule of three for the change of units, the mass of the book is 45600 miligrams.
First of all, the rule of three is a mathematical tool that helps you quickly solve proportionality problems.
Having three known values and one unknown, a proportional relationship is established between all of them in order to find the fourth term of the proportion.
If the relationship between the magnitudes is direct (when one magnitude increases, so does the other; or when one magnitude decreases, so does the other), the rule of three is applied as follows, where a, b and c are known values and x is the unknown to calculate:
a → b
c → x
So: 
Being 1 kg equivalent to 1000000 milligrams, In this case the rule of three is applied as follows: if 1 kg equals 1000000 milligrams, 4.56×10⁻² kg equals how many milligrams?
1 kg → 1000000 milligrams
4.56×10⁻² kg → x
So:

<u><em>x=45600 miligrams</em></u>
In summary, the mass of the book is 45600 miligrams.
Learn more:
Answer:We have , a relation in frequency f and wavelength λ of a wave having the velocity v as ,
v=fλ ,
given f=60Hz , λ=20m ,
therefore velocity of wave , v=60×20=1200m/s
Galileo is geocentric, just like all the rest of us.