Can someone help explain how to arrive at the answer (C) in depth?

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