Dear Bridget

Let's say James' working rate is x work per hour. In fact, x=1/8. Let's say Rachel's working rate is y work per hour. If they work together, then their working rate is x+y work per hour. 

x+y work / hour * 5 hour = 1 work, as given.

Therefore, x+y=1/5. Then, 1/8+y=1/5. Then, y=1/5-1/8=3/40. Hence, Rachel will spend 40/3 hours to finish the work.

Thanks,

Harim Yoo