Let:
T = number of toppings
P(T) = total price Sean will pay
B = Sean's budget
[tex]P(T)=9+1T[/tex]since the cost of the pizza cannot exceed Sean's budget:
[tex]\begin{gathered} P(T)\leq B \\ \text{Where:} \\ P(T)=9+1T \\ So\colon \\ 9+1T\leq B \end{gathered}[/tex][tex]P(T)\ge9+T[/tex]