error[E0369]: cannot multiply `f64` by `f64` in Rust

I am a Rust learner. I want to make a function that multiplies an euclid::Vector3D<f64,U> by an f64. I have this code:

use euclid::Vector3D;

fn main() {
    fn scale_vector<f64,Unit>(vec: Vector3D::<f64, Unit>, scale: f64) -> Vector3D::<f64, Unit> {
        Vector3D::<f64, Unit>::new(vec.x * scale, vec.y * scale, vec.z * scale)
    }
    enum Meters {}
    let vec = Vector3D::<f64,Meters>::new(1., 2., 3.);
    let scaled_vec = scale_vector(vec, 2.);

    println!("Original vector: {:?}", vec);
    println!("Scaled vector: {:?}", scaled_vec);
}

but cargo run gives me

error[E0369]: cannot multiply `f64` by `f64`
 --> src/main.rs:5:42
  |
5 |         Vector3D::<f64, Unit>::new(vec.x * scale, vec.y * scale, vec.z * scale)
  |                                    ----- ^ ----- f64
  |                                    |
  |                                    f64
  |
help: consider restricting type parameter `f64`
  |
4 |     fn scale_vector<f64: std::ops::Mul<Output = f64>,Unit>(vec: Vector3D::<f64, Unit>, scale: f64) -> Vector3D::<f64, Unit> {
  |                        +++++++++++++++++++++++++++++

Why? What is the way of doing this?

>Solution :

In fn scale_vector(), you added f64 as a generic type. Just remove it and it will compile:

    fn scale_vector<Unit>(vec: Vector3D::<f64, Unit>, scale: f64) -> Vector3D::<f64, Unit> {
        Vector3D::<f64, Unit>::new(vec.x * scale, vec.y * scale, vec.z * scale)
    }