Answer:
[tex]7\\\\9x-42=57[/tex]
Step-by-step explanation:
There can be any number from [tex]0,\ 1,\ 2......,\ 8,\ 9[/tex].
But by addition of that number and 42 should be divisible by 9.
[tex]42+50=92\ \ \ \ \ not\ divisible\ by\ 9\\\\42+51=93\ \ \ \ \ not\ divisible\ by\ 9\\\\42+52=94\ \ \ \ \ not\ divisible\ by\ 9\\\\42+53=95\ \ \ \ \ not\ divisible\ by\ 9\\\\42+54=96\ \ \ \ \ not\ divisible\ by\ 9\\\\42+55=97\ \ \ \ \ not\ divisible\ by\ 9\\\\42+56=98\ \ \ \ \ not\ divisible\ by\ 9\\\\42+57=99\ \ \ \ \ \ divisible\ by\ 9\\\\42+58=100\ \ \ \ \ not\ divisible\ by\ 9\\\\42+59=101\ \ \ \ \ not\ divisible\ by\ 9[/tex]
Hence only possible value in the gap is 7.
[tex]9x-42=57\\\\9x=99\\\\x=11[/tex]
