Let p be the number of people we want to host, then we can set the following equation:
[tex]C=780+9.75p\text{.}[/tex]Where C is the total cost. Therefore, if p=50 we get:
[tex]C=780+9.75(50)=1267.5\text{.}[/tex]If the budget is $1500, setting C=1500 and solving for p we get:
[tex]\begin{gathered} 1500=780+9.75p, \\ 1500-780=9.75p, \\ 720=9.75p, \\ \frac{720}{9.75}=p, \\ p=73.84. \end{gathered}[/tex]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.