Question $21$

Based on the Chapter $12$ lecture, Facebook's ad network customers are billed based on $$

Number of user engagements the ads receive $($e$.$g$.$ likes$)$

Number of times their ads are shown on Facebook $($CPM$)$

Number of clicks the ad receives $/$ total times ad is shown $($click$-$through rate$)$

$\%$ of sales generated from clicks of displayed ads $($CPA$)$

Number of times Facebook users click on displayed ad links $($CPC$)$

Question $22$