Knowing that when you throw something in the air, the speed will be 0m/s. The acceleration due to gravity is 9.8m/s^2.
v2=0 v1=24 a=9.8
The formula is: v2=v1+a(t) v2-v1/a=t 0-24/9.8 24m/s/9.8m/s^2=t (You can choose which direction is positive and negative) 2.45s=t t=2.45*2s (Since you calculate both going up and down) t=4.9s
