Answer:[tex]3 \mu s[/tex]
Explanation:
Given
Bianca is at [tex]x=600 m[/tex]
i.e. distance between origin and Bianca is [tex]600 m[/tex]
time taken to reach Bianca eyes is
[tex]t=\frac{600}{speed\ of\ light}[/tex]
[tex]t=\frac{600}{3\times 10^8}[/tex]
[tex]t=2\times 10^{-6} s[/tex]
[tex]t=2 \mu s[/tex]
i.e. Cracker exploded at [tex]t=2\mu s[/tex] because it is observed at [tex]t=4\mu s[/tex]
Time taken by second cracker flash to reach Bianca eyes
[tex]t_2=\frac{300}{3\times 10^8}[/tex]
[tex]t_2=10^{-6}[/tex]
[tex]t_2=1 \mu s[/tex]
Therefore it will be observed at [tex]t=3 \mu s[/tex]
