Janet can fill a certain order in 5 hours, therefore she performs 1/5 of the order within 1 hour.
Tom needs 8 hours to do the same job, therefore he performs 1/8 of the order within 1 hour.
Working together, they make 1/5 + 1/8 orders within 1 hour.
Let <em>t</em> mean the number of hours they need. Then we have equation: