ANSWER:
The ratio is 0.9 or 9:10
STEP-BY-STEP EXPLANATION:
We can calculate the ratio, calculating the quotient between the number of apartments and the number of bathrooms, just like this:
[tex]\begin{gathered} \frac{63}{70}=\frac{7\cdot9}{7\cdot10}=\frac{9}{10}=0.9 \\ 9\colon10 \end{gathered}[/tex]