Excel 2010 - Filling cell with blank cell using formula

In Excel 2010,

I've problem in filling a value with formula. Let me explain.

When a cell C3 is filled with value 50 , C4 should change to "paid", if filled with <20, C4 should change to "Pending". If C3 is empty, then C4 should also be an empty cell.

C3 = 35; C4= Paid; C3 = 17; C4= Pending; C3 = [empty]; C4= [empty];

for this which formula need to work on.

-thanks.