Doubt from chemical kinetics

chemical-kinetics
moderate
find-concentration
sequential-reaction
unsolved
pp
#1

#2

@Sneha_2021 please sand a clear image of your doubt so we can help you quickly.

#3

sir please download the picture then you may zoom it u will find it clear sir sorry for that i tried to click picture not able to get clear please see otherwise i will try post picture @Jangir sir @Shaquib sir...

#4