Temporary boost

In my 2D vertical platformgame i want to give my player a temporary jump boost.
im thinking something like.

if(hit.gameObject.tag == "Boost")
		{
		**var jumpheight =*2.0;**
yield.WaitForSeconds(5.0) destroy()

But im not sure how to put this in code.

Something like this should work:

public var jumpHeight : float = 5.0;
public var jumpTimer : float = 2.5;

function OnControllerColliderHit(hit : ControllerColliderHit) {
    if(hit. gameObject.tag == "Boost") {
        jumpHeight *= 2.0;
        Invoke("ResetJump", jumpTimer);
    }
}

function ResetJump() {
    jumpHeight *= 0.5;
}