Answer :
Remember that the rational numbers are those that can be written as a quotient of integers, this means the following:
[tex]\begin{gathered} \frac{a}{b} \\ a,b\text{ integers} \end{gathered}[/tex]in this case, 0 and 9 are integers, while 0.75 can be written like this:
[tex]0.75=\frac{75}{100}[/tex]cearly, 75 and 100 are integers, therefore, only 0.75 is a rational number