SUM.IF: Sum and divide values in two different columns depending on the value to the left

Hello again!

I've encountered one last problem before I can complete my work. In column C I have portfolio names, 1, 2 and 3 respectively. In columns E and F I have old stock price and new stock price, respectively. What I want to do is to divide the sum of the new stock price (F) with the sum of the old stock price (E) and take that sum minus one given that each cell value has the same cell value to the left (C). In cell F:120 to F:122 I then want these sums to be displayed, depending on which portfolio the return belongs to, with F:120 being portfolio 1, F:121 portfolio 2 and F:122 portfolio 3.

I have a feeling it has something to do with a sum.if formula, but since i am quite bad at excel I have no idea how to proceed. Please see the attached worksheet as it will make much more sense.

Grateful for any kind of help.