can someone help with an easy formula?

[satzzz]

I've attached the spread sheet in question. I have successfully completed one formula but i'm struggling with two more. If you open the file and look on the Net Promoter Score tab. Where the student numbers are listed and the numbers 0-6 are I have managed to enter the correct formula so that if on the Course Feedback (L&B & BSI) tab on question 12 on every students answer if 0-6 is inputted a 1 appears on the corresponding students number on the Net Promoter Score tab.That formula being =IF('Course Feedback (L&B & BSI)'!D17<=6,1,0)
Now I want to do the same if the student puts 7 or 8 and then another for the 9 and 10 area. For the life of me I just cant seem to foud how to add it to the formula for the 7+8 and 9+10.

Hope you can understand what im getting at. Can anyone help.