Speed= 72km/hr. what is the time to run 1.5km at this speed? explain

m just a sophomore in high school myself so i may get this completely wrong but here it goes.  
It seems that the answer to the problems is just to find average speeds. So for the first problem. The antelope is simply going half the distance of 1.60 km(.80 km) at 88 km/h. That means it has .80 km left. Because the problem gives you the average speed for the entire journey(67 km/h), all you have to do is find out what number averaged with 88 make 67. This number is 46. Take 46 and add 88 then divide by 2 (this is how you find the average of two numbers) and you get 67, so your answer is the average speed the antelope traveled at is 46 km/h for the second half of the journey.