Final answer:
Whataburger achieved its largest same-store-sales growth of +9% in 2003, indicating the company's successful growth strategies during that year.
Step-by-step explanation:
Whataburger experienced its largest same-store-sales growth in 2003, with an increase of +9%. This remarkable jump in sales reflects the company's success in attracting more customers and effectively boosting sales at existing locations. That year, Whataburger's concentrated efforts to improve customer service, expand menu offerings, and enhance marketing strategies likely contributed to this significant growth.