Welcome to our library book problem! We have three types of books in the library: story books, science books, and comic books. The total number is 420 books. We know that story books are 35 more than science books, and comic books are 28 fewer than story books. Let's use a diagram to visualize these relationships.
Now let's set up our variables. We'll let x represent the number of science books. Since story books are 35 more than science books, we have x plus 35 story books. Comic books are 28 fewer than story books, so that's x plus 35 minus 28, which equals x plus 7. Now we can write our equation: x plus x plus 35 plus x plus 7 equals 420.