Error Roll a Ball game - 2 of 8-Moving the Player

Roll a Ball 2 of 8
Moving the Player
Script error
this is my code
using UnityEngine;
using System.Collections;

public class PlayerController : MonoBehaviour {

public float speed = 0.0f;

private Rigidbody rb;

void Start ()
	rb = GetComponent<Rigidbody> ();
void FixedUpdate ()
	float moveHorizontal = Input.GetAxis ("Horizontal");
	float moveVertical = Input.GetAxis ("Vertical");

	Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);

	rb.AddForce (movement = speed);

error "Cannot implicitly convert type ‘float’ to ‘UnityEngine.Vector3’

I am just a biggner so please provide me solution as soon as possible.

Line 16, you’re setting a movement variable of type Vector3 to a float(local field to the class), did you mean to multiply the movement by the speed?

 rb.AddForce (movement * speed);