Consider the question. Emily spent X dollars on Friday, twice that amount on Saturday, and then three times X on Sunday. Over the three days, she spent $120. What is the value of X, in dollars?
 If the answer is '20'; explain the reasoning:
She spent X dollars on Friday. She spent 2X dollars on Saturday. She spent 3X dollars on Sunday. X + 2X + 3X = 120. 6X = 120. X = 20.