What is the best way to solve the following problems:

Sam's family eats 4 to 6 apples every day. Which is a reasonable number of days that it will take Sam's family to eat a bag of 20 apples?

Terry's party started at 6:30 p.m. and ended at 9:00 p.m. What was the total amount of time that Terry's party lasted?

20/5 = ?

9 - 6.5 = ?