area of the cube is given by
[tex]A = 1.9 * 1.9[/tex]
[tex]A = 3.61 m^2[/tex]
now the area covered by one micrometeorite
[tex]A' = (1 * 10^{-6})^2[/tex]
[tex]A' = 1* 10^{-12} m^2[/tex]
now we will find the time to cover this area
[tex]t = \frac{A}{A'}[/tex]
[tex]t = \frac{3.61}{1* 10^{-12}}[/tex]
[tex] t = 3.61 * 10^{12}s[/tex]
now we need to fill the whole cube
so the height required to be filled
[tex]T = \frac{1.9}{1* 10^{-6} * 3.61 * 10^{12}[/tex]
[tex]T = 6.86 * 10^{18} s[/tex]
[tex]T = 2.2 * 10^{11} years[/tex]
so above time is required