Two friends, Haley and Kristen, 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. Haley's hair is already 19 centimeters long and grows at a constant rate of 1 centimeter per month. Kristen's hair is 11 centimeters and growing at a speed of 3 centimeters 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? How long will that take?