Name Error for all codes

I am consistently getting a name error the codes I run in all the optional labs. It keeps showing the variable name used is not defined. Same thing happens for my assignment as well. Please do tell me a solution for this.

Thank you

Are you running the lab in Coursera Labs? Or on another platform?

When you open the lab, you alway must run every cell starting from the top.

A screen capture image of your error would be helpful.