141. Find all values of the digit $a$, if the number $\overline{a 719}$ is divisible by 11.
$\triangle$ Divisibility of this number by 11 is equivalent to the divisibility by 11 of the sum $a-7+1-9=$ $=a-15$. The difference $a-15$ is divisible by 11 only when $a=4$.

Answer: 4.