How did you call your function ratio() in the previous exercise? Do you remember the two ways to specify the arguments? (If you have forgotten it might be useful to review the video from Intermediate R)

You probably either did ratio(3, 4), which relies on matching by position, or ratio(x = 3, y = 4), which relies on matching by name.

For functions you and others use often, it's okay to use positional matching for the first one or two arguments. These are usually the data to be computed on. Good examples are the x argument to the summary functions (mean(), sd(), etc.) and the x and y arguments to plotting functions.

However, beyond the first couple of arguments you should always use matching by name. It makes your code much easier for you and others to read. This is particularly important if the argument is optional, because it has a default. When overriding a default value, it's good practice to use the name.

Notice that when you call a function, you should place a space around = in function calls, and always put a space after a comma, not before (just like in regular English). Using whitespace makes it easier to skim the function for the important components.