document.getElementById("buttons_quest_5").style.display = 'none';
            document.getElementById("quest_5_formula").style.display = 'none';
            quests[4] = 1;
        }
    } else {
        document.getElementById("reply_quest_5").innerHTML = "It has an infinite number of solutions. Planes' intersection is a line. Every point in this line is a valid solution.";
    }
}

function done_system_4_quest_6() {
    if(last_iterations == 58) {
        document.getElementById("reply_quest_6").innerHTML