The pollutions levels of a city were monitored throughout a day. The pollution levels are shown in a graph; answer the following question based on the graph:-

What was the pollution level in the afternoon, at $4$ o'clock?
 

The pollutions levels of a city were monitored throughout the day. The pollution levels are shown in a graph; answer the following question based on the graph:-

What was the change in pollution level from $12$ o'clock noon to $6$ o'clock in the evening?
 

The pollutions levels of a city were monitored throughout a day. The pollution levels are shown in a graph; answer the following question based on the graph:-

By how much did the pollution level decrease from $1$ o'clock at night to $4$ o'clock in the morning?