Excel 2007 : fetch data from a cell address when the address is user supplied

Dear All,
I need to set the contents of a cell on my worksheet (named 'report card') to be same as contents of a cell in another worksheet(named 'log sheet'). This is easily done.

But the problem is, the address of this cell in 'log sheet' (from where data will be fetched) will be dynamically given by the contents of a cell (based on user supplied data) on the present worksheet. For example, I have typed 61 in cell N11 in worksheet 'report card'. Then I need cell B13, to have the contents of cell F61 of 'log sheet' . Again if the contents of cell N11 changes to say 91, then call B13 should be populated by data from log sheet cell F91. How does one do this ? I am attaching part of the document in question.
I need urgent help on this. Would be grateful if anyone can help.