var table = document.getElementById("homework-table");
var rows = table.rows;
table.rows[0].cells[2].setAttribute("colspan", "2");
for(var i=1; i<=rows.length-1; i++) {
            var td = document.createElement("td");
            td.innerHTML = "x";
            td.classList.add("remove_lesson");
            table.rows[i].appendChild(td);       
        }