Learning about proportions

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.

Drag each tile to the correct box. not all tiles will be used. arrange the steps to solve the equation . simplify to obtain the final radical term on one side of the equation. raise both sides of the equation to the power of 2. apply the zero product rule. use the quadratic formula to find the values of x. simplify to get a quadratic equation. raise both sides of the equation to the power of 2 again.

6/y=9/24 whats the proportion? a= 16b= 19c= 20d=21