The gravity is decresing vertical component at rate of 9.80 m/s because gravity acceleration is 9,80 m/s^2
Simply by deviding starting vertical speed and gravitational acceleration we get time required for projectile to stop gaining altitude.
90/9.8 = 9,18s
Looking at the answers there isn’t 9.18 offered as answer. But it is indeed answer for the question that has been asked. Maybe you thought that 49m/s is vertical speed than the answer would be 49/9.8=5