Let x be the number of toppings and y be the cost of the sundae. We know that a sundae costs $2 without any toppings, and each topping costs $0.50. Therefore, the equation that describes the relationship between x and y is:
y = 2 + 0.5x
This equation can be represented on a graph, with x on the horizontal axis and y on the vertical axis. As x increases, y increases by $0.50 for each additional topping. The graph will be a line with a slope of 0.5 and y-intercept of 2, meaning that the line passes through the point (0,2) and rises by $0.50 for each unit increase in x.