Question 1203345
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if -1 is added to a number and the sum is doubled, the result is -18 less than the number
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n, the number

{{{2(n+(-1))=n-(-18)}}}---------LITERALLY!  Description tells exactly this.


Simple algebra...


{{{2n-2=n+18}}}
{{{n-2=18}}}
{{{highlight(n=21)}}}