Gravity is affected by mass and distance
To solve this problem we will apply the concepts related to Reyleigh's criteria. Here the resolution of the eye is defined as 1.22 times the wavelength over the diameter of the eye. Mathematically this is,

Here,
D is diameter of the eye


The angle that relates the distance between the lights and the distance to the lamp is given by,

For small angle, 
Here,
d = Distance between lights
L = Distance from eye to lamp
For small angle 
Therefore,



Therefore the distance is 5.367km.
1) First of all, we need to find the distance between the two charges. Their distance on the xy plane is

substituting the coordinates of the two charges, we get

2) Then, we can calculate the electrostatic force between the two charges

and

, which is given by

where

is the Coulomb's constant.
Substituting numbers, we get

and the negative sign means the force between the two charges is attractive, because the two charges have opposite sign.
Answer:
Mg will replace Ag in a compound
Explanation:
A single replacement reaction is driven by the position of ions on the activity series.
As a rule of thumb, the position of metal ions on the activity series determines their reactivity.
Metal ions that are above another are more reactive and they will displace those that are lower.
Generally, activity increases as we go up the group.
Mg ions are higher than Ag ions on the series so, Mg will displace Ag from a solution.