Question 753794
Let d = denominator
Let n = numerator.


First sentence means, {{{d=3+n}}}, so the common fraction is {{{highlight(n/(n+3))}}}.


IF {{{5/28+n/(n+3)}}}, THEN {{{abs(1-(n+3)/n)}}}.  We want to find or solve for n.


The positive value of the difference is part of what we want to use, so let's just write the value in its expected positive form:
{{{(n+3)/n-1}}}
which we could simplify
{{{(n+3)/n-n/n}}}
{{{(n+3-n)/n}}}
{{{3/n}}}


What should be done with that?  Back to the whole second sentence and the symbolic meaning of IF,THEN...
{{{highlight(5/28+n/(n+3)=3/n)}}}


You should expect better results continueing from that equation, so the rest is being left for you to try (but be sure to understand the path to the last highlighted equation first).