20. Andrei was asked to name the apartment number that his family received in the new building. He replied that this number is 17 times greater than the number in the units place of the apartment number. What is the apartment number?
20. If the desired number is $10 a+b$, then $10 a+b=17 b$, from which $5 a=8 b$. The equality is possible only when $a=8$ and $b=5$. Answer: 85.