Answer:
C. Mario should have multiplied the x-values by $6.50 to get the y values.
Explanation:
Let's do it the way they said. If we were to multiply 1 by 65, it would be $65. If we did the same thing for 2, 2 x 65 is $130. This is incorrect because these values do not match up with the ones on the graph.
Decimal points are important in this case because it completely changes your answer. When you multiply 1 by 6.50, you get 6.50. Which is what's on the graph. Multiply 2 by 6.50 and you'll get $13, and so on.
So now we can conclude that the mistake Mario made was that he multiplied x by the wrong value (65), when it should have been $6.50.
Note: Hope this helps! Good luck on your test. :)