Exponential function is characterized by an exponential increase or decrease of the value from one data point to the next by some constant. When you graph an exponential function, it would start by having a very steep slope. As time goes on, the slope decreases until it levels off. The general from of this equation is: y = AĆb^x, where A is the initial data point at the start of an event, like an experiment. The term 'b' is the constant of exponential change. This is raised to the power of x, which represents the independent variable, usually time.
So, the hint for you to find is the term 500 right before the term with an exponent. For example, the function would be: y = 500(1.8)^x.