Drill 20: Why this way — Variables and mutability

fn main() {
    let title = "Variables and mutability";
    println!("{}", title);

    let mut minutes = 12;
    minutes = 14;
    println!("{} minutes", minutes);

    let rating = 4;
    let rating = rating + 1;
    let rating = rating as f64 + 0.5;
    println!("rating {}", rating);

    let price: f64 = 19.99;
    let published: bool = true;
    let grade: char = 'A';

    const MAX_LESSONS: u32 = 100;
    println!("{} {} {} {}", price, published, grade, MAX_LESSONS);
}