Solve 6+5c-2c+7-c equation

Find the missing dimension! need asap! tiny square is a =3025 in ²

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.

Identify reflection rule on a coordinate plane that verifies that triangle a(-1,7), b(6,5), c(-2,2) and a’(-1,-7), b(6,-5), c’(-2,2) triangle are congruent when reflected over the x-axis