Afighter plane lands on an aircraft carrier at a speed of 300 km per hour takes 25 seconds to come to rest. determine its landing speed in meters per second

When I saw the part about "25 seconds to come to rest", I thought
you were going to ask for the acceleration during the roll to a stop. 
But you didn't.  That fact isn't needed in order to answer the question
that you did ask.

You said that his landing speed is 300 km/hour.

    (300 km/hr) x (1,000 m/km) x (1 hr/3,600sec)  = 

             ( 300,000 / 3,600 )  (m / sec)  =  83-1/3 m/sec

                                                         (about 186 mph)