Hello,
please refer to the hints given just below the grader cell. See what have missed based on the template code given at the start of the uploaded notebook. These assignment require you to just replace None with the right code with the help of hints given.
Make sure your variable like how @elirod mentioned has been recalled by the right code.
dj_dw and dj_db codes need to be written in single line code. So check your hints and find how you can write this code in single line.
Regards
DP