Initial velocity u = 20 m/s
Initial horizontal velocity = 20 cos30° = 20 * 0.866 = 17.32 m/sec.
Initial vertical velocity = 20 sin30° = 20 * 1/2 = 10 m/sec.
time taken t = u/g = 10/10 =1 sec. ( approximating g to 10m/sec^2)
Maximum height h = ut + 1/2 * g * t^2
h = 10 *1 - 1/2 * 10 * 1* 1
h = 10 - 5 = 5 metres.
Total time in air = 2t = 2 seconds.