Simplify the following text for a Grade 4 native English-speaking person.
Original: Suppose that x and y are real numbers and that y is a function of x , that is , for every value of x , we can determine the value of y. This relationship is written as : y = f ( x ) .
Simplified: Let 's say we have a function y = f ( x ) . f is short for function , so this equation means `` y is a function of x '' .