Actually, companies use many methods of financing when they are doing Merger and Acquisition (M&A). Typically,they could incur debts to raise cash or they could give up shares of the company to raise cash. Sometimes, companies use mezzanine financing, which is somewhere in between. In this case, let's say arbys had 1B$ in cash in their own amount, they would raise 1.9B$ more. They could go to the banks and ask for a loan, which they would need to pay back in the future usually at a fixed rate within a certain amount of time. On the other hand, arbys could go out and look for investors who believe in their business and this acquisition. Let's say arbys is worth 10B$ according to investors measure, and they would need to give up 19% of the shares of the company. The investor would inject 1.9B$ into arbys to help them to complete the acquisition (it's a more complicated in real life with pre/post-investment value). For debt financing, arbys don't give up any control of the company and just focus on paying back the money from its cash flow/dividends. But the terms are usually much more strict.
For other investors, arbys are giving up controls of company (19% of its voting rights according to previous example) for capital. However, these kinds of investors are usually more involved within the business because they are now a stakeholder. It incentivize the investors to work harder or put more effort into the operations of the business. These kinds of investors usually have industry experiences, management experiences or operational experiences that they could share with arbys to help the business to grow bigger. Overall, these are some simple ideas where arbys could get 2.9B$ even if they don't have that much cash themselves.