One benefit of the single index model is that the number of required estimates to calculate the efficient frontier decreases significantly compared...

9. One benefit of the single index model is that the number of required estimates to calculate the efficient frontier decreases significantly compared to the general Markowitz framework. How many estimates do you need to calculate the efficient frontier using the single index model when you have 60 risky assets to invest in?

(a) 60 (b) 180 (c) 182 (d) 1770 

Anyone can explain step-by-step and in depth on why it is C?