Answer:
[tex]x_{cm}[/tex] = 4.6 10⁶ m
Explanation:
The definition of mass center is
[tex]x_{cm}[/tex] = 1/M ∑ xi mi
Where M is the total mass, mi and xi the mass and position of each body
Let us apply this equation to our case, as they indicate that we take the center of reference to Earth, its distance is zero; let's write the data they give us
Earth
M = 6.00 10²⁴ kg
r1 = 0
Moon
m = 7.35 10²² kg
r = 3.80 10⁵ km (1000m / 1km) = 3.80 10⁸ m
Let's calculate
[tex]x_{cm}[/tex] = 1 /(m + M) (0 + m r)
[tex]x_{cm}[/tex] = m / (m + M) r
[tex]x_{cm}[/tex] = 7.35 10²² / (7.35 10²² + 600 10²²) 3.80 10⁸
[tex]x_{cm}[/tex] = 4.6 10⁶ m