Project: A/B Testing for ShoeFly.com

Hello,
I’m trying to solve task #7 in the A/B Testing project:
https://www.codecademy.com/courses/learn-r/projects/r-aggregates-shoefly

This is my code:

clicks_by_experiment <- ads_clicked %>%
  group_by(experimental_group, ad_clicked) %>%
  summarize(count = n())
clicks_by_experiment

However, when I save I receive two errors:

Error in group_by(., experimental_group, ad_clicked): object 'ads_clicked' not found

and

Error in eval(expr, envir, enclos): object 'clicks_by_experiment' not found

Can someone help me understand what I am doing wrong?