AP physics hw help?

Question

hi, i understood these problems during class, but now that i'm doing the hw, i'm completely lost.

question 1: According to a rule-of-thumb, every five seconds between a lightning flash and the following thunder gives the distance of the storm in miles. Assuming that the flash of light arrives in essentially no time at all, estimate the speed of sound in m/s from this rule.

question 2: A horse canters away from its trainer in a straight line, moving 130 m away in 14.0s. It then turns abruptly and gallops halfway back in 4.8s. Calculate (a) its average speed and (b) its average velocity for the entire trip, using "away from the trainer" as the positive direction.

question 3: An airplane travels 2100 km at a speed of 800 km/h and then encounters a tailwind that boosts its speed to 1000 km/h for the next 1800 km. What was the average speed of the plane for this trip?

I already know the answers, but I need help figuring out to work the problems.

answers:

1: 300 m/s
2: 10.4 m/s 3.5 m/s
3: 4.43 hr 881 km/hr

Answer 1

1.If the light is instantaneous and the sound travels .2 miles/second, simply convert miles to meters and you have your answer. Since 1mile =1609.344 meters, the speed of sound is estimated at 322 m/s

2. The average speed is the time it took to traverse the entire distance:
(130+130/2)/(14+4.8)

The average velocity is
(130/14)-130/(2*4.8)

3. the first leg took 2100/800 hours = t1
the second leg took 1800/1000 hours = t2

the average speed is
(2100+1800)/(t1+t2)

j