Summation in VBA

Never used VBA before, but I want to write a simple code to calculate the following equation, anyone know how to do this the most efficently?

"i" will always be 1, but I want to be able to manipulate the 3 variables n,TFi and Q (TFi is one variable in itself)

The JPG of the equation is attached, let me know if it doesn't work for some reason...