Katrina and Amanda are studying in the same class. On Monday, Katrina solved 35 math problems and Amanda solved 21 math problems. On Wednesday, Katrina solved 16 math problems and Amanda solved 20. On Thursday, Katrina solved 40 math problems and Amanda solved 24. On Saturday, Katrina solved 18 math problems and Amanda solved 24 math problems. On which day did Katrina and Amanda have the same ratio of problems solved as Monday?