in declaring variables of part, why return area test error?

[labike]

pub fn calculate_area() -> u32 {
    // TODO: Implement the function here
    // Declare width and height as immutable variables
    // Calculate the area of the rectangle
    // Return the calculated area
    let width: u32 = 10;
    let height: u32 = 5;
    let area: u32 = width * height;
    return area;
}

in declaring variables of part, why return area test error, and not everyone use area? the error from "test_variables"