Given the recursive rule for an arithmetic sequence, enter the explicit rule. f(0) = 7 and f(n) = f(n − 1) + 8 for n ≥1

The explicit rule is f(n) =_
for n ≥ _

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.