please i need help for the last question. C file for calculating the area of a rectangle. thanks

1. Use your own words to describe the process of a program development 2. Use your own words to explain the purpose of the following directive in the helloworld program: #include 3. Use your own words to explain each part of the following compile command gcc -o hello helloworld.c 4. Attach the c file of calculating the area of a rectangle we built during class time