Answer:
Part 1) 
Part 2) 
Step-by-step explanation:
Part 1) Find the value of x
we know that
Triangles CDF and FDE are similar
therefore
The ratio of its corresponding sides is proportional and its corresponding angles are congruent
so


Part 2) Find the length of DE

substitute the value of x

An=a1+d(n-1)
an=nth term
a1=first term, when n=1
d=common differnce=amount each term increases by
n=which one
so
when n=1, an=40
so a1=40
it seems to increas by 7 each time
an=40+7(n-1)
explicit formula is expanded
an=40+7n-7
an=33+7n is the formula
the domain is natural numbers because you can't have the -3rd term or the 0th term or the 3.24th term
domain is natural numbers
the formula is

or
C. Is the answer to this question
Answer: I think it's C
Step-by-step explanation: