Uniform motion problems: Problems where an object moves at a certain speed, or rate

Ex3: Mirasol took a non-stop flight to visit her grandmother. The 750 mile trip took her 3 hours and 45 minutes. Because of bad weather, the return trip took 4 hours and 45 minutes. What was her average speed for the round trip?

Ex4: A railroad switching operator has discovered that two trains are heading toward each other on the same track. Currently the trains are 53 miles apart. One train is traveling at 75 miles per hour and the other train is traveling at 40 miles per hour. The faster train will require 5 miles to stop safely, and the slower train will require 3 miles. About how many minutes does the operator have to warn the train engineers to stop their trains?

Homework p. 174 #10,19-21,26,30,31