The initial velocity is 0 km/hr , the final velocity is 24 km/hr and the time is 3 s what is the acceleration?

Take note that acceleration is the rate of change of velocity with respect to time. So to solve it, take the difference between the initial and final velocity. Then, divide it by time it took for the velocity to change from its initial to final value.
a= (Delta v)/(Delta t)
a= (v_f - v_i)/(Delta t)
a=(24 (km)/(hr) - 0(km)/(hr))/(3s)
a= (24 (km)/(hr))/(3s)
In order for the unit to be consistent, change the time from seconds to hours.
a= (24 (km)/(hr))/(3s* (1hr)/(3600s))
a= (24 (km)/(hr))/(1/1200hr)
a = 28 800 (km)/(hr^2)
Therefore, the acceleration is 28800 km//hr^2 .