If this is all the info you got from the client .Then i wouldn’t say it as an estimate but considering giving them a ‘guesstimate’ which would take say somewhere from 80 to 200 hours (even more or even less) .And once you get further details then you can start doing some ground work by breaking down each requirement and then work on the estimate .Which still can vary by as much as 20- 30% .
And to your original question ‘How many hours’ i think that is something no one can answer with exact figures because it all depends upon how much knowledge you have and how ready your resources are(people you need to work for proving spec,test data,testing etc) are.
In the past i worked on projects where the project estimate and actual hours varied by 100%.
Hope this helps!
Thank you,
Anil
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