Excel 2007 : Calculating Productivity

Hey everyone - I'd really appreciate some help

I attached a file showing the format that I needed for the Productivity calculation.

Where I have given the Number of tasks achieved in one hour in B Column,

And what I needed is When I input the number of task alloted field in C, the result should be displayed in the D column in hours depending on the productivity of Column B.

Thanks in Advance.

Let me know if you have any questions.