Alfonso is trying to move a new sofa into his apartment. Unfortunately, he forgot to measure the size of his doors and it turns out the sofa won´t fit through! He must therefore lift the sofa from the street and bring it into the apartment through his window. The sofa has a mass of 160Kg. With a rope Alfonso can pull upwards with a force of 400N. Calculate how much mass Alfonso can lift alone. State whether he will need to ask for help from his friends, and if so, how many friends will he need to ask?