step 1: \ \

Initial velocity of pebble is 35.0 m/s .

Final velocity of the pebble is 33 m/s.

Find the maximum height :

The pebble is trown with an initial velocity.

Consider the kinematic equation .

Where v is final velocity,

             u is initial velocity,

              g  ( 9.8 m/s² ) is acceleration of gravity.

Find the time at which pebble attains maximum height  : .

step 2:

Now find the maximum height by kinematic equation .

Solution :

The maximum height reached by pebble is 6.938 m.