The price of a personal pizza, \( y \), can be expressed as a function of the number of toppings, \( x \). Since the base price for a plain cheese pizza is $7 and each additional topping costs $2, the equation can be written as:
\[ y = 7 + 2x \]
This equation shows that the total price \( y \) is equal to the base price of $7 plus $2 for each topping \( x \).