A function is a tool within mathematics that takes an input, performs a series of operations and then gives an output. The notation for a function takes the form: f(x) = algebraic expression. Here, f is the name of the function and x is the independent variable. Any algebraic expression can be on the right of the equals sign. None of the answers are particularly satisfactory in this case, but (d) is the closest: distance(time) = 800. The main problem being the independent variable is not on the right hand side of the equation.