HELP; Need advanced math to Excell formula...

First, Excel does not do the needed looping for these types of series calculations. Ideally, you can find a simple formula that does not require the looping. For example, the summation for i=1 to n is equal to 0.5*i*(i+1), which is much easier for Excel. Failing that, you will need to either create a table that steps through x to y and then sum the answers for each step or resort to VBA.

Second, your equation needs more definition. Usually, summations identify a max and min, but also what variable is changing over the summation. You state this is a summation from x to y, but there is usually a variable, such as i, that is being changed for each integer between x and y, inclusive.

Finally, I do not know what "y over x" is as an advanced math function. To me, it means, y/x, which is not very advanced.