Thuyết trình về vấn đề trang phục học đường

17 a tourist was planning a trip by car for travelling at some constant speed for 2.5 hours. however, he found that if he increases the speed by 20 km/h he can cover the same distance in 30 minutes less time than it was planned. what was the planned speed of the tourist, in km/h?

Jerrold has to buy 12 copies of a textbook which costs $36.25 per copy. how much must he spend for them?

What does the first stage of a multistage rocket do?