Let,

u = Initial velocity of stone

H = Maximum height attained by the stone

v = final velocity at maximum height = 0

t = time taken to attain maximum height = 3 s

a = -g = acceleration due to gravity

(i) We know that,

v = u + at

0 = u – g × 3

u = 3g = 3 × 9.8 ms^-2

u = 29.4 ms^-1

(ii) From the equations of motion, we know that,

H = 132.3 m