The daily rate for a hotel room that sleeps 4 people
is $39 for one person and x dollars for each additional person. If 3 people take the room for one day
and each pays $21 for the room, what is the value
of x?
(A) 6
(B) 8
(C) 12
(D) 13
(E) 24
What is the algebra for this question?