<div class="block">
<div class="priceday">10</div>
<div class="form-text">20</div>
<input class="summ" type="text" name="summ" class="form-text">
</div>
$('.block').click(function(){
var price = parseFloat($(this).find('.priceday').html());
var day = parseFloat($(this).find('form-text').html());
sum = day * price
$(this).find('input.summ').val(sum);
}).trigger("click");