Two friends, Emma and Alice, are growing out their hair. They plan to cut it off at a certain point and donate it to a charity that makes wigs for people with cancer. Emma's hair is already 10 centimeters long and grows at a constant rate of 2 centimeters per month. Alice's hair is 30 centimeters and growing at a speed of 1 centimeter per month. If the girls get their hair cut on a certain day, they will have exactly the same length to donate. How long will their hair be?