Answer:  
 or
  or 
 or
 or  
 or
 or  

Explanation:
Since, According to the question,
For each pound the operator’s guess differs from the contestant’s weight, the contestant will receive $3.
And, If a contestant weighing x pounds received $15
Then the guessed weight of contestant = 

But, Again according to the question,
The guessed weight is 120 pounds,
Thus, 

⇒ 

⇒ 
 (by multiplying 3 on both sides)
 (by multiplying 3 on both sides)
⇒ 

⇒ 

⇒ 
 ( On dividing both sides by 3 )
 ( On dividing both sides by 3 )