need more step by step 1

I attached the original questions and the step by step answers I was given. Can someone give me more detailed step by step? There seems to be something missing. For example on question 13, how do you get from the original function to the line below where it’s factored? Where did the -16 come from all of a sudden? These are good but I need ALL the steps so I can understand what happens in between them. Please don’t combine steps or skip anything. All the little details and steps help me a lot. I need questions 13, 14, 17, & 18