To find the total number of customers who responded to the survey, you simply need to add the number of customers who preferred the old coffee cake muffins to the number of customers who preferred the new cornbread muffins.
Total customers = Number of customers who preferred old coffee cake muffins + Number of customers who preferred new cornbread muffins
Total customers = 8,131 + 6,543 = 14,674
Therefore, the total number of customers who responded to the survey is 14,674.