Please help mathematics 8th grade

1. what are the missing reasons in the proof 2. it's in the second picture and 3

Find the midpoint m of z1=(8+5i) and z2=(12+3i)

Acar started driving from city a to city b, distance between which is 620 miles, at a rate of 60 mph. two hours later a truck left city b and started moving towards city a at a rate of 40 mph. how many hours after the truck's departure will the two meet?