Question 1024204
Initial number, {{{10t+u}}}.


This is the description translated into a system of equations.

{{{system(2t=17+abs(t-u),10u+t-(10t+u)=9)}}}


The difference equation becomes {{{10u+t-10t-u=9}}}
{{{9u-9t=9}}}
{{{highlight_green(u-t=1)}}}.


Handling the absolute value equation gives these two possible equations:
{{{system(t-u+17=2t,or,-t+u+17=2t)}}}
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{{{system(t+u=17,or,3t-u=17)}}}.



Either or both of the results of the absolute value equation may work.  Start with the "non-negative" form to remake the system.
{{{system(u-t=1,u+t=17)}}}.
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Add corresponding members...
{{{2u=18}}}
{{{u=9}}}----------which indicates {{{t=8}}}.



Original or initial number should be  89.