Two tailors, Annie and Gabby, sit down to do some embroidery. Annie can embroider 4 shirts per hour, and Gabby can get through 5 shirts per hour. In addition, the tailors had previously finished some shirts. Annie has already completed 15 shirts, and Gabby has completed 10 shirts. Annie and Gabby decide to take a break when they have finished the same total number of shirts. How long will that take?
