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?