byCar is a function that returns a method. You have to invoke the method. You can use double parentheses to invoke it immediately.
return `To travel ${distance} Kms costing is Rs. ${fn(distance)(distance)}`;
I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.
You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.
See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).