Final answer:
Cross-selling is the strategy for growth in which the firm encourages existing customers to buy more of the firm's current product.
Step-by-step explanation:
The strategy for growth in which the firm encourages existing customers to buy more of the firm's current product is cross-selling. Cross-selling is when a company promotes additional products or services to their existing customers to increase sales and customer loyalty. For example, a fast food restaurant may offer a combo meal that includes a burger, fries, and a drink, encouraging customers to buy more items.