Question 1044142
The job of 1 document, shared between two computers?  The application is impractical.  As just a RATES exercise, 1 whole job is "print the document".

<pre>
                   RATES, Jobs per minute

Slow Computer     {{{1/(x+15)}}}

Fast Computer     {{{1/x}}}

Together           {{{1/4}}}
</pre>

The variable assigned to time for the fast or new computer to do 1 job is x.
{{{1/(x+15)+1/x=1/4}}}
Solve this for x.