function changeDivImagea() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea3a.jpg)"; 

} 

function changeDivImageb() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea3b.jpg)"; 

} 

function changeDivImagec() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea3c.jpg)"; 

} 
function changeDivImaged() 

{ 

    document.getElementById("display").style.background = "url(./portfolio/hea3d.jpg)"; 

}