Final answer:
Using a linear attribution model, each of the four ads the customer clicked before making a purchase gets equal credit. Therefore, the last display ad would be assigned $25 from the $100 purchase.
Step-by-step explanation:
The question involves understanding how a linear attribution model works in digital marketing. The customer visited the site four times and various ads contributed to the final purchase of $100. Using a linear model, each touchpoint (in this case, ads) receives equal credit for the sale. Since there are four visits, each one contributes equally to the conversion. Therefore, we divide the total sale amount by the number of touchpoints to determine how much conversion credit the last display ad would receive.
$100 (total sale) / 4 (number of touchpoints) = $25 conversion credit per touchpoint
So, the conversion credit assigned to the last display ad is $25.