We have been given that Jenna saves $3 for every $13 dollars she earns. Vanessa saves $6 for every $16 she earns.
We can compare the ratios of saved money to earned money by Jenna and Vanessa as:
Let us simplify our equation.
We can see that 
, therefore, Jenna's ratio of money saved to money earned is not equivalent to Vanessa's ratio of money saved to money earned.
Since you want to cancel something out, the book makes the 24 3 times eight so that both of the threes can be canceled out
