As new store owners, they had to carefully watch cash flow. As their customer base began to grow, they began offering hot food, and hired others to help with the operation. The economic benefit created in this story is called An Invisible Hand
Explanation:
Invisible hand refers to an economic term that is used to describe the unexpected benefits of a business venture which was started with the sole purpose of self benefit but later on that benefit is also enjoyed by the community as a whole
This clearly states the economic benefit which was unexpected in the business.
In the given Scenario also, the couple occupied the business but, the benefits were completely unexpected and the growth rate was also high as related to investment made.
Thus, the correct phrase for such situation is:Invisible Hand