[Paramasivan]

I have done with the following code:

$('#plusexp').click(function() {
    var $cols3 = $('.cols3');
    if ($cols3.is(':visible')){
        $('.cols4').show();
    };
    $cols3.show();
});

The following code also works :

$('#plusexp').click(function() {
    if ($('.cols3').is(':hidden')) {
        $('.cols3').show();
    } else {
        if ($('.cols4').is(':hidden')) {
            $('.cols4').show();
        }
    }
});