Problem in Week 3 programming assignment - predict didn't defined in previous cells

Hello @Shokoofeh_Khani,

We lock ungraded cells in all assignment. If you wonder how to handle error that appears in a locked ungraded code cell, you may want to take a look at this FAQ.

As for the problem you are encountering, as @gent.spah and @YijinChen suggested, since predict is your exercise 4, you need to first run the code cell containing it in order to define it, before running any subsequent code cell. Also, each time you re-open a notebook, please make sure to run all the code cells from the top.