Yolanda says 105 is the same as 50 because 10x5 equals 50. what was yolanda's mistake

 Yolanda's mistake is that she is assuming 105 is same as 10 x 5 .

Explanation:Here 105 represents a three digit number where 1 is at hundreds place,0 is at tens place and 5 is at once place and it can be written as the product  of its factors 5 and 21 i.e 105=5×21 =21+21+21+21+21+21=105(by adding once place and tens place), where as 10×5 represents 5 times number 10 i.e.10+10+10+10+10=50(by adding once place and tens place)

So ,assuming 105 is same as 10 x 5 is her mistake.

i believe it is c.y = 9x

rise over run. 9 units up over 1 unit right or 9/1