Asupermarket chain gathers data on the amount they spend on promotional material (e. g., coupons, etc.) and sales revenue generated each quarter as a result of those promotions. the predictor variable is?

The predictor variable in this problem is the amount spent on promotional material.

Explanation: 

A predictor variable refers to variable needed to make a prediction of another variable. If we analyze the problem, we notice that the supermarket chain is predicting the sales revenue generated because once the supermarket spends on promotional material, it will result to sales revenue. Thus, the predictor variable is the amount spent on promotional material.