The average of 3, 5, 15 and my number is 40. what is my number.

Ineed with number 17 i don’t get it at alll

If olu is twice as old as funmi if the sum of their ages is 60 how old is olu

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.