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This is a simple question if you remember when we were discussing kinetics , the half life of only first order kinetics was independent of the initial concentration.
Zero order kinetics and second order kinetics their half life depends on initial concentration.
In the given question the change in concentration from 0.60 sec  to 0.30 sec is 30 seconds and from0.30 to 0.15 again only and 30 seconds,
So here the half life is constant it means this reaction is first order kinetics and depends only on the concentration of ester.

It does not depend on the concentration of water because water is here taken in excess as a solvent. So that is the reason it is also called as pseudo first order reaction.

now in the second part of the question they are asking us to calculate the average rate of the reaction between 30 to 60 seconds -Average rate of the reaction is the change in concentration divided by total time.
Now you can try it and post your answer here .