Question 885907
r = the rate of each machine in JOBS per HOUR.
The description and question imply that 1 job will be done with the two machines.  The question asks for finding r.


RT=J rate, time, job


First seven hours, both machines.
{{{(r+r)*7}}} = amount of job done after both machines.


Last fourteen hours, only one machine.
{{{r*14}}} = amount of job done using only one machine.


The sum of those two amounts of job are 1 whole job.
{{{2r*7+r*14=1}}}
{{{14r+14r=1}}}
{{{28r=1}}}
{{{highlight(r=1/28)}}}-----ONE JOB IN 28 HOURS, the rate of one machine.