The 24 students in ms lee's class each collected an average of 18 cans for recycling the 21 students in mr galvez's class each collected an average of 25 cans for recycling how many more cans were collected by mr. galvez's class than ms lee's class

The perimeter of ? cde is 55 cm. a rhombus dmfn is inscribed in this triangle so that vertices m, f, and n lie on the sides cd , ce , and de respectively. find cd and de if cf=8 cm and ef=12 cm. the answer is not cd=20 and de=15. i have tried that one, it does not work.