Let p be the number of people we want to host, then we can set the following equation:
![C=780+9.75p\text{.}](https://img.qammunity.org/2023/formulas/mathematics/high-school/mu2l3ihl2nyvu64z2nl4d11s8px8w0vx3o.png)
Where C is the total cost. Therefore, if p=50 we get:
![C=780+9.75(50)=1267.5\text{.}](https://img.qammunity.org/2023/formulas/mathematics/high-school/6tnstyi92ssu6j86omx6zb6l5u4a5257by.png)
If the budget is $1500, setting C=1500 and solving for p we get:
![\begin{gathered} 1500=780+9.75p, \\ 1500-780=9.75p, \\ 720=9.75p, \\ (720)/(9.75)=p, \\ p=73.84. \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/bgi5humdvgianf33vzivyex7ne4zjt58ji.png)
Therefore, you can invite 73 people.
Answer: The total cost to host 50 people is $1267.5. If the budget is $1500, you can invite 73 people.